1. When you notice that an older prof has died their hair.
I always think that profs just live in their heads, coming up with brilliant things in brilliant places. In between that lecture they did over at MIT or Sorbonne, they went to shopper's drug mart and picked up a box of hair dye! They're human too!

2. Singing in my room all alone. Mariah, you better watch out

3. saying ETHIDIUM BROMIDE. It makes everyone sound like they have a lisp