Taunting penalties can be completely subjective and officials from the same crew may even call them differently. BUT....when you stand up, look down at the defender, and then drop the ball on him, that's pretty much textbook taunting. JuJu got it for a clean hit and then standing over Burfict while staring at him. That's taunting. Gesturing at the opponents sideline is a taunting penalty. While it is a very subjective penalty, there are some things every player should know is most likely going to draw a flag. I don't think mixing it up with the fans should be though, as long as there is no actual profanity use or physical touching.