In the film Reservoir Dogs, the character Mr. Pink goes on a rant against tipping (I haven't included a link because it is, after all, a family blog). I have to say I agree with some of his rant, particularly the part about being obliged to tip when the service doesn't merit it.
The jars assume everyone and every job is tip worthy. It just ain't so.
I will say however that whoever thinks of the "tip jar humor" may be deserving of a tip.
You make the call: here are a few examples: