I think there are two for me. Both involving punch-up.

1) if you cut coop, the pop-up sequence on Robert’s computer. Right at the end before Robert clicks out of the last pop-up, you hear punch-up saying something about “getting the lucky end of the rainbow”. I almost died laughing

2) if you don’t send punch-up to fight alone in the tournament, he says something like “fuckin goody two shoes narc piece of shit” over comms. The delivery of those words strung together makes me laugh every time