So my husband brought up a good question the other night as I had the Viz Dub of the first season playing in the background while we did chores.... Why does Mamoru pick on Usagi and act pretty much kinda socially awkward in the first season and then after that it's like he get a complete personality change?

I didn't have a really good answer besides perhaps him being reborn and their memories being reset but...if he was reborn and no memories wouldn't he have picked on Usagi in the Makaiju Tree Arc like he did in the first season? He doesn't really do that.

So...thoughts? Theories?

I kinda chalk it up to the memory reset (and bad writing of his character in general of the anime, even though I absolutely adore dorky 90s anime Mamoru, the writers clearly didn't bother to give him any real development past season 2).

Maybe because Usagi doesn't respond the same way as she did in first season. In first season, she kept on feeding insults back to him, but in the Doom Tree arc, she pursued him, and maybe off-screen he tried to annoy her but she didn't react with her usual annoyance, so he back off from her.

They definitely made him way less playful and teasing. :< I think he started to get less so during the rainbow crystal arc? Especially the princess revelation episode - he was trying to be playful with her but he didn't exactly pull it off. I think his realizing he was Tuxedo Mask and coming face to face with death probably weighed him down and got him thinking about what he wanted out of life and all that; when his memories were erased during doom tree arc all that life/death development went with it, and when the memories returned so did those revelations: Life is short. The love of your life fights evil on the regular and actively states she doesn't want to do that but is trapped into doing it anyway. You guys could die at any moment, and that sucked so hard last time that the world restarted. Twice. Ish. At least yours did. 

SO, excluding terribad development for bestboy, he could've just realized how much she meant to him and so dropped the issues and just went all chill and there for her aka cardboard cutout >C

edit: ha ha haaaa i only just now got that you meant during doom tree arc not after, lmao. I'M WITH OTHER POSTERS if his memory was wiped I mean back in the first arc he met a girl, teased a girl, got a GREAT reaction out of that, and thought "that was fun, I'll do that again!" but this time??? way too forward rando middle school girl acts way too close way too fast and, frankly, that's a can of worms mr. top-grades doesn't want to open but keeps getting offered over and over again.

For specifically the makaiju arc, I wonder if... his memories were reset, but his feelings weren't? So originally him and Usagi would both mess with each other as a mutual thing, and all of his memories are from that, but he find himself feeling more connected to her. At the same time, since she's acting closer to her, that could lead to a disconnect that just makes him act. Weird. He's not willing to accept development that he doesn't remember, so he won't start dating her, but at the same time, he can't go back to acting like he did before.

...I'm honestly not sure if that even makes sense or not.

Out of Story?  Bad Writing. Just, terrible. They had no idea what to do with him after the first two arcs. (kinda like what they did to Usagi for two arcs to develop Chibiusa and put their characterization on the back-burner or for one-off episodes where a Lesson Must Be Learned.)

In-Story:  I agree that maybe it was his lingering feelings, but I also think he's not always like that all the time. I mean, to be honest, I'm not a fan of 'playful insults/teasing' because I just don't like that sort of thing and it can turn hurtful very fast and very easily.  That aside, I think Mamoru has -always- been chilled on the regular. It's just that, his first meeting with Usagi was like and he was -only- like that with her because it's probably the only way he communicates with her on that level after multiple meetings- it's all they've ever done at that point to a point.

So, when the second arc comes around, he's without his memories, but Usagi doesn't respond as she had before and is trying to get him back, therefore, there's no need to act the same way. 

I mean, it's not really a personality change so much as he's just responding differently because it's more successful to do it that way.  He still teases Usagi but it's different and not as frequent.  (Like the episode in Super, where she's thinking they're going to make out in an abandoned house, but really he just wanted her to see these kittens and held one up to her puckered lips for it to lick her.  That's cute and playful in my book. )

After all, considering how many friends or people he knows that shows up in the series, he can't be that socially awkward a lot.

Aah, yeah I didn't think about the way Usagi was acting could also affect how he acted around her. Cause now that you all mention that, I recall him being nice to Rei, no picking on her, in the first season (but also was kinda indifferent to her and seemed very oblivious about the situation? like he was just trying to be nice and didn't realize that she liked him? XD) so perhaps it was just how Usagi and his personalities clashed during that time.

I also kinda forgot how he tones it down a bit once the Rainbow Crystal arc starts. I think I'll pay more attention to his mannerisms this watch through and see what I think once I get past the first season.

Yep.  But also, remember that Rei wasn't purposely trying to antagonize him or that their meeting was argumentative at all.  She's never sarcastic with him when they met, is what I mean. (I don't even remember when they met, but I do remember there wasn't any conflict, really, to their relationship.)

You could say the same about Usagi's interactions with Rei too.  The only reason the two fight is they constantly bait each other into it. If Usagi did not respond or if Rei didn't respond to the bait, they probably wouldn't argue much, if at all.

I think on a level, both Rei and Mamoru respond to sarcasm with sarcasm, and once that particular tone is set, that's just how it's going to work out to a degree. (Rei's just more proactive/playing up the Red Is Passion archetype to a degree.)  Mamoru decreases his teasing, I think particularly after the whole Nephrite/Naru Arc, when he sees just how genuinely upset/worried Usagi was over Naru after Nephrite's death.   It's a side of her he definitely hasn't seen before, so that might be the point of him changing gears there because it's like "Wait- she...really is caring and trying a lot. Maybe we don't have to do this???" 
(But I could be projecting, but it seems like that a bit? It just seems that, the moment they stop baiting each other and having actual conversations, the less need for teasing.)

<<;  but that's just my two cents about i.