Whenever my friend comes over we always like to play on my Xbox of PS3 or sometimes stuff on my PC.
I don't mind my other friends going on, since they don't do what this one does.
If he goes on MY PS3 or Xbox he changes all my avatar stuff, changes this little comment thing (psn) sometimes messages my friends, makes a new user (PS3), or if my Flash drive is plugged in he browses it. (This is why I hid it somewhere). If hes on my PC he mostly just checks his facebook or plays one of my games, but sometimes he looks through my pics or my history. Other times when we are in my basement (where my TV and game systems are) he likes to dig through stuff that we are cleaning out so he can find some games or something I think I may have lost.
Tl;Dr: IMO I hate people digging and changing my personal stuff.