You know nothing about this man. Please don't judge them based on a casual comment in a forum. That's cruel.
You know nothing about what I know about this man. Please don't judge my accurate assessment.
Are you trying to imply that you know this person? That your assessment is informed by direct experience of interactions with them in the settings he describes?
If not then the null hypothesis should in fact be that your assessment is anything but accurate.
Even the dullest of innocent jokes, delivered horribly, can get a chuckle in decent company. "Falls flat" means the "jokes" are inappropriate, mean, gross, *ist, etc. The phrase "colleagues or the opposite sex" is a tell.