There are always tough clients, but I'd say we at the LA Bicycle Kitchen have a conversation about asking someone to leave maybe every 6 months.

If possible, "taking a break" is preferable to full on banning. For one, it's not practical for us to ban someone for life, and an unenforceable threat just turns it into a Mom said no, go ask Dad situation.

Have someone who is on good (least bad) terms with the client have a one-on-one conversation, outside of the shop in case there's a scene and to emphasize that they (or better yet, their behaviors) aren't welcome by the group. Try to be clear that you are acting on the groups behalf, it's not that "Joe says you can't come anymore".

Something like:

"We think that you've (taken things knowing it's against the rules | acted aggressively towards volunteers | taken advantage of us in some specific way). As a group we want you to take a break from the space. If you come back in the next month, you will be asked to leave."

I prefer this because it's reasonable to enforce, while still giving some real consequences to a person that maybe just feels invincible. Also, it gives them a path to be on good standing with your group in a month.

Immediately, I can think of three people that we've asked to take a break like this. One of them (a few months ago) hasn't come back. A second stayed away for 6 months or so, and now seems to be happy to follow our rules, and the third is back and raising hell all over again. Your mileage will vary.