What is the one thing at work you hate more than anything?

There's a guy I work with. Whistles maniacally. To everything. Even the commercials. Off tempo, adds in his own improvisation. Whistles guitar solos. He sings too. Off key, too high, wrong lyrics, starts singing the second he recognizes the tune. He has on several occasions sung the lyrics of one song to the tune of another. It's like 12 years of daily bad karaoke....