I can understand your worries and it's hard to simply bury them. I would certainly let your friends know that you have sensed a vibe from this guy and to just be aware.

I have a total biker dude neighbour who gets grief because of the image he has and the attitudes that people take towards bikers. Funnily enough, though, he's one of the most down-to-earth, open-minded and kind people in the neighbourhood.