A recent one for me.
Spoiler: Just bad experience
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A friend of mine, whom is a player in my current 3.5 D&D game happened to have his house alone for the day and offered to host for the days session. We all accepted and one of the players was already there. We have played at his house before, which was why we agreed. Another player whom doesn't game with us as often due to distance but is always a welcome member to our group, because he dives right into a character whether support or main and we all have a good time when he comes to play, informed he'd like to join us and would roll up a temp cleric for a support role since he wouldn't be able to make it to every session.

Time comes we all arrive at my friend's place and find another friend there we'll call him F, it was his neighbor so it wasn't too surprising, except that I thought he would be at work at the time. I had not invited F to play in the game prior. I had my reasons, he can be disruptive at times as a player and it also made my gf (plays the rogue in our group) a bit uncomfortable as they had a bit of a falling out on their friendship the year before.

On the only suitable table we have for gaming at my friend's house(plays wizard in group), there is also the setup for a hookah on the table. It seems that's what Wizard, F and our other player(monk) were doing in addition to mariokart waiting for us to show up. One of the players was our ride (duskblade). So we go to get the game set up and started. I had an npc, a bard whom I was going to have left out of the session, since our temp cleric was going to cover back up healing and support. Again F is disruptive, and starts smoking the hookah and invites Monk, Wizard, Temp Cleric and Duskblade to join in. Temp cleric refuses and wants to focus on the game, so do I. Unfortunately due to how the hookah was set up, my gf and I keep getting smoke blown in our faces. Granted they do realize this and try to adjust it or blow it away from us not to much avail. My gf had to switch seats to be away from the smoke. Only F continued with the Hookah for awhile, then became disruptive showing me things on his phone.

Now as it was not my home, I would not be in the right to just ask him to leave, more so since F had been there prior to our arrival. F had never met Temp Cleric prior to this day and his chihuahua syndrome, semi napoleon complex I guess, started showing up. He pulled out his pistol to show people, left it visible in front of everyone and then put it back where he had it. The only way to get F to stop being disruptive was to allow him to play the bard I had as a temp, so that I wouldn't be guilted by F into being a hypocrite for letting Temp cleric play and to just get on with the session and get the day over with.

The sad thing is, the behavior unnerved Temp Cleric and he has yet to show up to another session, though it may be as much part due to the time it takes for him to come up and hang with us as well as what occurred.

For those of you who would ask, yes it was loaded and he did have a license to carry it.