E! News has exclusively learned that the That Awkward Moment star went to The Hollywood Improv for the Laffest show on Sunday evening.
According to an insider, Efron was with one gal pal and one male friend and mostly "kept to himself."
"He was drinking a green tea and shared nachos and wings with his group," the eyewitness added. "He seemed very relaxed and was laughing throughout the show."
We're told that the group arrived around 7:30 p.m. and left only a few hours later.