I don’t base any of my characters off of real people, because, frankly, everyone I know is either so normal that it isn’t worth it, or so out there that I wouldn’t know how.
The thing about normal is that once you’ve met one, you’ve met them all. I already know what normal people think about every subject, because they all think and do the same things (quite deliberately, too). Hence, the whole normal part. If I write a normal character, he’s going to be based on the conglomerate of normal behaviors, rather than any specific individual.
Then there are the weirdos, who have wild anecdotes and even wilder beliefs. These are the people who are fun to talk to, because I don’t know what they’ll say or do next. That unpredictable element also makes them impossible to write, because I don’t know what they’ll say or do next. Can’t write what I don’t know.
All of my fictional characters are just that: fictional. I draw heavily from my personal study of psychology, but I never have any specific people in mind.