John Carpenter brought real "homeless folks" into the production for several scenes and smaller characters and gave them food as well as paychecks. "I thought that was a pretty classy thing to do," said Roddy Piper.
The line "I have come here to chew bubble gum and kick ass, and I'm all out of bubble gum" was ad-libbed by Roddy Piper. According to director John Carpenter, Piper had previously written the line in his notebook of potential verbal bits during his wrestling career. He shared the notebook with Carpenter, and they agreed that this particular line fit the character and the film perfectly. Piper went on to use it at a wrestling match.
The big fight sequence was designed, rehearsed and choreographed in the back-yard of director John Carpenter's production office. The fight between Nada (Roddy Piper) and Frank (Keith David) was only supposed to last twenty seconds, but Piper and David decided to fight it out for real, only faking the hits to the face and groin. They rehearsed the fight for three weeks. Carpenter was so impressed he kept the scene intact, which runs five minutes, twenty seconds.
After Nada kills several ghouls and exits into a side street he comes face to face with a human cop whom he disarms and tells to leave. The actual phrase he uses is "Beat your feet," but according to Piper the actor apparently misinterpreted it on the first take and began running in place. "God bless him," he says, "his heart was into it big time."
Roddy Piper, being a married man at the time of filming, refused to take his wedding band off. That's why in several scenes you can see a wedding ring on.