[That ian guy]

I am learning sign language slowly because my girlfriend's stepfather is deaf... I don't think that counts for "dating someone with a disability" question...

They really are looking for a reaction when they make fun of him... Which honestly, I don't know how people could make fun of people with disabilities without remorse... The only time I did make fun of this guy with a deformed arm was because he was a complete asshole to me for no reason...
I'm guessing since your dating a deaf person, you know a pretty good ammount of sign lanuage... Personally, I'd "mouth off" about your friends in sign language, so your boyfriend can get a laugh at them (that is, if they make fun of him in front of him)