I think Sam panicked about losing control of the situation. He's usually the puppet master in these cases. Imagine sitting there, you're 6'2, you're the leader of your group, the smartest and most masculine guy. You're supposed to represent your new show that cost a million dollars to make. And this little 60 year old boomer is single handedly destroying your whole posse with ease. You can see Sam's annoyance mount when Harland starts making his Christian rape van joke, just look at his face.