reminder that a common mamamad tactic is to block the instance owner before joining, either to make kicking him harder or make noticing him harder. simply go to the small social menu (the "Here" tab) in the one-handed quick menu (NOT the big one), and scroll all the way down. if you're the instance owner you can see people who blocked you and kick him from there.
reminder that mamamad also crashes instances and you should probably just kick him on sight anyway even if he "isn't doing anything wrong" at that moment. he can also rejoin an instance on an alt without being friends with anyone once he's been in that instance at least once before, because friends+ instances are basically "open" and public, just hidden. if he keeps coming back you'll have to kick him and then drop a portal to somewhere else and he won't be able to find you.