Some people are not self concious of what effect they have on people.
I have a friend that makes conversation difficult because he can't reign his mind in to stay on the subject. He also speaks sooooooo fast it is difficult to comprehend what he is saying but then again, maybe it's my hearing.
If he is a true friend, you can politly tell him your concerns.
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"It doesn't cost "nuttin", to be nice". 
MOM
I just want to do the right thing! Uncle Joe, (my hero).