How old are his friends? I think common response has to be taught too; they may just look at you because you are odd in their experience for thanking them or trying to talk to them; maybe they're use to girlfriends that are just eye candy or shy or don't speak? Conversation, which can feel and seem obvious to us isn't necessarily to other people, especially sometimes young guys?

We have a 19 year old next door neighbor guy that helps us old folk and he's perfectly nice, well educated (going to school to become an engineer or architect) but won't "talk", even when you ask him a question he'll not respond but just look at you, LOL. Over time it has gotten a little easier to sometimes get him conversing but my husband still hasn't gotten the knack and will ask me, "Did you get Tri to say anything?" Some people are just like that, not experienced or skilled in conversation (yet).