My coworker Joey and I have a giggle habit of laughing at anything that might also entertain a 9 year old boy (coincidence that I HAVE a 9 year old boy? I think not.). Only way these words are funnier than standing alone is when they are used during a normal, serious conversation, like a client meeting. The quieter we're supposed to be, the funnier they seem. I know there are more....but its 1:45am on a Tuesday.
Poop (heavy emphasis on the "oo" sound)
Stoo-pit (as said by Nicole Portman)
do do (especially as said in a meeting "Yes, when we do do that tomorrow.......")
Balls (funniest all by themselves)
Duties (singular "duty" is equally as effective)