You know Chris, you're a genius! Why don't we just have adults post here! And everyone under 18 can close their accounts!
Adam (Smartypants) felt insulted, because you just posted the image. If you would've included that you thought it was funny, maybe he wouldn't have reacted the way he did. He must've reacted the way he did, because he felt offended, and you insulted him, when he was just trying to defend someone. I know he shouldn't have said "STFU", but still that doesn't seem like a good reason to suspend someone. But it's your site, you can do whatever you want with it.
Regardless of the reason for the reaction, Adam is responsible for reacting that way. Plus, reacting to a sick burn by saying "STFU" is sort of Jr. High School.