Barber gave me an evil look?

I've been going to the same barber for about 2 years because he's the best in town. He's a real straightforward, quiet dude but sometimes I manage to get a little conversation out of him. Well today I walk in to the shop and while he was cutting someone elses hair he stopped and stared me down with the most evil look for like 20 seconds. I really don't know what his deal is, I tip him pretty good and I asked him if he wanted me to come back another day but he mumbled something which sounded a no so I stayed. But man, I've never had someone look at me like they wanted to kill me before, should I find a different dude to cut my hair? What's his deal??