The two most common retards for me:

When I was in the 50s, warlocks trying to kill my group with Seed of Corruption. The first time I got owned by that because I wasn't watching. Every time after that I kept an eye out and... 5x grounding totems. LB LB LB LB dead 70

And also when I was in the 50s, I think like 5 or 6 different rogues (in my level range) tried to gank my main. It's like... yeah, my 4 others are looking right at you. If they had any intelligence they'd sap an alt while I was running (and maybe not notice it), or blind my main and have a go at a follower... or not just unstealth around me ;)