Beedrill and Vespiquen. But that's only because I have a phobia of bees/wasps/hornets in real life. D:
Also, Mr. Mime scares the crap out of me. If I'm playing my LeafGreen, I sometimes yell at my screen "OMFG KILL IT STARMIE KILL IT!!" If it's Emerald, I'm probably saying the same thing only...