Thankfully "laughter" is a really strong thing that we can use anytime, either make the dad laugh with things like :
Make a grouchy face and saying "Sad magician is sad"
. Or things of the like I don't know, make him lauhg and you will win him out.
But most probably, if he is your's girlfriend dad, most probably he is testing you out, seing how much can you endure, so you are qutting doing magic in front of him because you are afraid he will mess up things? then I don't think that will look good to him.
Play the odds and the circumstances to your advantage, you already know that the guy is a heckler and that he will grab your deck, build a routine around that, anticipating his moves, I do not mean Brian Tudor's Heckler routine, but hey, if the guy is predictable, use that to your advantage and build a routine that plays off when he takes the deck away or things like that, I do not know if you get my drill but try it.
Be creative