Behold the power of the apostrophe, as demonstrated with a line from The Safety Dance:

Case 1: ...we can leave your friends behind.
Case 2: ...we can leave your friend's behind.

Which presents the perfect segue to an item we sell at work that rather amuses me because...well, see what you think. Perhaps it's just my guttermind at work here. ( Notice that there's a thermometer on this thing as well. )