Firstly, were there anyone around in your friend's place at that
time? if his parents or family members were around, then i guess u
were just a tool for them to release their tension! cos his family
members wouldnt think that they would do it when their friend is
around.
If lets say there is no one at your friend's house, then all i can
say is that...Close one eye la Brudder! they just had the urge and
had the necessary facilities to release it! u were just a
"spectator" they have no regard for!
who knows....put urself in your friend's shoes, u would do the same
thing given the same situation arises? ya? 
