Earlier tonight, I edited a question. About 10 minutes later, the OP edited again and (IMHO) made the post worse. Is it OK to rollback OP's second edit to my version -- Or does that break some sort of unsaid Stack Overflow etiquette?
No, his editing was awful, a rollback is fine, but at some point I usually just let it go if the OP doesn't want to make his post better. If you do roll it back, make sure and check all he did to not miss any clarification that he might have also put in.
Actually, it'd probably be better just to re-edit what he did.