1. Talking *really* quietly
2. Talking *really* fast (note: both 1 and 2 apparently make it difficult for people to understand me at times)
3. Not making eye contact
4. Making random comments/non sequitors
That's all I can think of. #3 my brother told me in high school, #2 and #4 friends told me in college, and #1 I should have guessed at by how many times I was asked to speak more loudly, but I wasn't told explicitly until grad school. I've improved greatly with #4 and to a limited extent with #3, but I find #1 and #2 hard to control, and anyway I can't perceive when I am speaking too quietly or too quickly so trying to correct these habits has been somewhat pointless.
Then there are some other random odd things, like I remember one time when I was a little kid and I was hitting the wall in groups of three (3 is a special number for me) as my family was walking along, and my mom told me to stop or people would think I was weird. My mom also always hates my knee-jiggling, and always makes me stop.
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Not all those who wander are lost... but I generally am.