So listeners to FtB have probably heard about the "Dome of IC" that one of their Gm's used to invoke back in the day. A unique approach to handling an everyday gaming issue. This combined with the following example led me to wonder what idiosyncrasies you or your GMs have exhibited. Good, bad or (ideally) amusing; please share. I'll start.

One of my good friends who was our long time gm had a particular way of introducing characters. If they were friendly or generic they would say "Hi" or "Hello" or some other generic opener. If they were evil or at least shifty he would always say "Greetings" in an overly dramatic manner. This became a major tell which we naturally teased him over. Now having been made aware of this he did try to mix it up and even exploit our awareness. However he would always slip into old habits as time went on.

I never sit down when I'm GMing. This is because I have bad hips, and my GMing style is active; if I sat, I'd be having to get up. It's easier and less painful to just never sit down.

Sounds like Gygax was a bit of an odd cookie:

For some reason I find that whenever I GM I always have a short table. This could either be my main surface to work off or it's a supplementary table for my notes. This not location based at all and is not intentional it's just a weird coincidence.

My current GM will break to tell some very off-color jokes. This has even happened in the middle of rather intense combat sequences.

I actually didn't use a grid when running the game, until I bought myself a Chessex playmat. Before that, all positioning was fast and loose, and players could run at the speed of plot.

I stand whlie GMing unless it's combat. Then I sit down and start working through my various notes.

Also a combat thing, but I tend to turn into a super villain while running. I tend to yell at my NPCs, fling their sheets over my shoulder when they die, and all sorts of ridiculous things.

If it's a sci-fi or modern day game, I'll also send emails in real time. Something happens two days before the next session IG? My players get an email from their goons warning them that it happened. That sort of thing.

killing everyone constantly

That's an idiosyncrasy? I thought that was the GM's job

I stand frequently when gming unless I really need to read my notes at that moment. There is always a character named Lorenz in my game world no matter what and he is always a badass that shows up at a pivotal plot encounter. I also don't use a play mat but that's because I mostly play modern or sci-fi settings and everyone is using guns so there is no chance of a random attack of opportunity from moving.

I like to stand/pace when I GM as well.