I was a customer this time, and for some reason, I just decided to poke the bear. I stuck my nose in, pointing out that coupons expire for a reason, and there was NO law requiring the store to accept it.
Custy: "You know what? Fuck you!"
Me: "No thanks, you're not my type."
Custy: "I wasn't inviting you, bitch, I'm saying FUCK YOU!
Me: "And I said YOU'RE NOT MY TYPE!"
Custy: "Are you fucking stupid?!"
Me: "You're the one arguing with me over the context of this conversation..."
Custy: "Fine, go fuck yourself!"
Me: "I have a boyfriend who does the job just fine, thanks."
Custy: "ARGLEBLARGLE FUCK OFF AND DIE!"
Me: "I don't respect you enough to take your advice. And you're still arguing with me about this."
He finally realized that there was no way to win and just stormed out, swearing like a sailor.