HOWEVER, there's a huge difference between a harmless prank and betraying someone's trust to be mean to them. I consider keylogging and pwning someone's machine deep into the in the "asshole" category. I also think that jerking someone's mouse when they are trying to click is not clever, just annoying, not funny. Especially because it could more effectively be done physically. It's in the same league as tripping someone when they walk by - just dick behavior.
A prank is something the pranked can laugh at, not just the pranker.
Since I was just leaning to explore my sexuality during that time and my IM messages and emails reflected that I'd be pretty horrified to know someone stole my password, pwned my machine, and read them. Like, seriously horrified and very violated.