I just got done arguing with someone who said Button was just a self insert, and it made me realize exactly how I write Button Mash, and kind of why I'm one of the rare (and first) DiamondMash shippers.

I write him like a teenager who is still a child. Romance and sex can enter his mind, but they're never at the forefront. Instead, he focuses on his video games and the fun he can have. He is an almost eternal optimist, looks at things bright and colorful, and also very simple, such as, "You've done nothing wrong to me, so why would I hate you?" And that sort of childish attitude can be something other characters can like and cling onto, especially if their life is a bit on the rough side.

How do you guys write him though, especially in a way that makes this shut off nerd having friends make sense?

Well as someone who doesn't wright at all (though really wishes he could but can't for crap) my opinion doesn't matter that much. Honestly though, you could write him in a variety of ways but your seems the best. Someone whos trying to figure out life but is a shuddin, a teenager with child like innocence, nerdy but sympatheitic, a simple kind soul, but can have if only small burst of rage. Man i wish i could my words onto paper Button is like my fav backround pony wish i could wright. Well thats my two bits.
Side note i love DiamondMash