The funniest glitches (at least to me) have both taken place on rocks.
In the first glitch, I was standing on top of a rock in Bonfire Island. I did the Howl action, and for some reason the rock didn't like it. I sank into the rock slowly, almost like a ghost.
In the second glitch, I got stuck in a rock platform at Ascension Island upside down with my legs sticking out of the surface.