Why don't you play some pranks on him? Have at least a little bit of
fun for all the misery he's put you through.
Get green paintballs and put them in the shower head. They dissolve
with the hot water very nicely. Mix his shampoo with food coloring, and
pour some liquid garlic in his shower gel.
Cut holes in the underwear he leaves in the bathroom, and staple his
socks together.
Don't get mad, get even!