We only tip citizens’: Grandfather of server sends angry Facebook message to diners who left note on

As much of a cheap jerk he was, at least it the bill didn't automatically add 18% gratuity, I hate that!
I was at a Tex-Mex place. I order beef fajitas. When they brought me shrimp fajitas I sent them back. When everyone else was almost done with their meal they brought me half shrimp-half chicken fajitas. I sent them back again. When they brought the bill 20 minutes later they brought my plate of beef fajitas along with it (and the bill had the upcharge for the shrimp on it too!).
Since everyone else was ready to leave, I sent it back again and asked for my fajitas to be removed from the bill. They did, but they still kept that 18% gratuity on there, and for what?!