One seems to understand the humor, but is Super Duper Serious about whether the signs are "legitimate" and refuses to play. The others are probably not checking that thread any more so even explaining the point isn't making a dent in their skull densities

One did finally click after Mr Happy explained it, though I did make a dig at that one at the same time, and figure that also drove him/her/it away.

The super-serious ones just make me shake my head, and wonder if there's anything other than The Cable Guy that makes them laugh or even chuckle...