I hate any surface that is shaky or wobbly in any way. Especially chairs and tables that are uneven and shake from side to side. This fear goes back to when I lived in CA and went through the Loma Prieta earthquake of 1989, also known as "The Big One." After I was traumatized by that as a kid, I have hated shaky things with a passion. I hate being in portable classrooms, I hate it when someone sits behind me and shakes my desk by tapping their feet on it, I will switch chairs in class until I find one that has 4 even legs, the same with tables at a restaurant (I will move, or get coasters to try to put underneath to steady it).
A funny joke that my friend played on me because she knows my fear:
My freshman year roomate took my bed (which was up on cinderblocks) and took 2 of the cinderblocks away and just balanced the bed on the remaining 2...the top left and the bottom right. So the next time I went to go sit in my bed, the entire thing collapsed, I started screaming hysterically and my roomates just sat there laughing. I still have yet to get her back for that. Luckily she's my roomate again this year...any ideas?