Never. I've only really been banned once on any server, and there was good reason behind that ban. (I actually did break a rule, and it was by no means a dumb rule. That was when I first got this account. I originally didn't intend to use it seriously.)
I'm very, very picky about the servers I join. I've only seriously joined a select few with the intention of actually getting involved in the community and enjoying the servers. Any others were just a "troll around with friends" day where I never came back to the server. (It's been a long time since I've last done that, now that I think about it...) I've never really joined any servers that ban for "stupid reasons," at least not for long enough to get banned, anyway.
Honestly, the only communities I've seriously had any involvement in are this one, the Hive for a short period of time, and one other place that I won't speak of in detail. (For a number of reasons, really. I'm very careful about giving out server names. Let's just say it's nothing like MCSG, and searching "G33ke" or any variant you can think of that relates to me on google won't find it for you.) None of these said communities have dumb rules/staff, so I'm lucky enough to have never really...been banned for almost anything.