isn't "deal with it" and its various incarnations considered dismissive
This info may be inaccurate:
If it was said right off the bat, like the second time I got banned (I.E. "I play BlockLand more than minecraft thread), than it's dismissive. If you're telling someone who you are arguing with to get over something, deal with it, etc., it's a more aggressive way of telling them to calm down, which is what my intention was during the argument.
TL;DR: it is dismissive if you're telling that to someone who is arguing with someone else.