I'm pretty tolerant of other cyclists except when they use "your" instead of "you're" or "there" instead of "their" -- then they get the cinzano treatment
I think the worst uninvited drafter I can remember caught me after 125 miles, and I was dragging. I saw him getting out of his car, so I didn't think about him. Next hill, he misses a shift and scares the living crap out of me.