haha. i always warn my friends that i'm playing music after they invite me to skype. my friends have to endure my music while i'm on skype with them. i turn it low obviously, but they always make comments about how they can hear like "i'm in space."

edit: i don't do it to be a douche. i specifically ask if they're all cool with it. they don't mind. someone below suggested headphones, sometimes yes. but i use headphones strictly for skype (all i hear is people talking in skype through headphones) then use speakers for music. i have a subwoofer, so i have to use it with my speakers.