Back when I was in college, I was young and dumb enough that I'd login to AIM on the college computers. (Nowadays I won't login to personal accounts on anything I don't fully control. I'm always surprised by coworkers who check their bank accounts, social media, personal email, etc. on their work laptops.)

Anyway, even at the time I was pretty good at logging out when I left each computer, but once I forgot. The next time I logged in, I was surprised to discover that my entire buddy list had been cleared. I never understood the motivation behind doing so. I don't think it was particularly funny but, even if it were, it's not like the perpetrator got to see my reaction or even to point and laugh.

I did learn a lesson from it, but presuming that that was the mission of whomever did it feels ... Generous.