Anything involving worker rushes... Those probes can do some serious damage to my drones if I'm not careful. bastards. After the initial annoyance it's easy to completely stomp the opponent, though. ^^
I am so nydus rushing my 1v1 practice partner (who likes to FE with P) with queens and drones/spines and type "I heard you like bases to I built a base in your base".
My sister used to pwn gold league players with her probe rush oO she won like 80% of her games with that