The tumor is when you have one testicle showing outside of your pants/shorts, you then turn to an audience and ask them " Does this look like a tumor? ". The audience will look down at your ball sack and then they say "what the fuck man" and then you laugh at their stupidity.
Nick: "Hey Rob does this look like the tumor?"
Rob: (looking down) " What the fuck man, why you gotta show me your sack?"
Nick: "Hahahahahahahaha dumbass"
the act of pulling your balls out through your open fly and squeezing them so they turn shiny and purple while simultaneously getting someone to look at it.
As i showed her the tumor laughing uncontrollably, i yelled look at this shit.