Some stereotypes I rather dislike:
-EVERY fangirl/fanboy is rabid.
-All overweight people think only about food.
-A woman's place is in the kitchen. (If some dude said this to me, I'd beat the living crap out of him.)
-All excitable kids are automatically diagnosed with ADD or ADHD.
-Asians are experts at math. (Granted, I'm not Asian, but I do have a few friends of Oriental descent, and they absolutely HATE this stereotype.)
-People who wear glasses are really intelligent. (Even though this would seem like a compliment, it would also mean that in a job, you would be expected to understand and solve problems within a timely manner.)
-All people who lift weights only dine on red meats or are unintelligent.
-All people labeled as "geeks or nerds" have horrible acne, speak with a lisp or wear glasses.
-All science majors are nerds.
-All people who live in rural/country areas are either stupid or farmers.
-All farmers speak with a Southern American accent.
-All people who wear black are either emo, goth, or punks. (No ALL black mind you, just a tee shirt.)
-All people who play Pokemon, Yu-Gi-Oh, Digimon etc. are immature.
-All college students who live in dorms on campus drink, smoke, play guitar, or have sex frequently.
-All gamers are anti-social pricks who are unintelligent.
-All African Americans carry a gun.
-All Italians like pasta, or are mobsters.
-People native to Mexico are unhygienic.
-All gay people wear neon colors or carry murses.
This isn't a stereotype, but more of an observation. I find it rather interesting that a lot of people seem to confuse stereotypes with pet peeves.