Well, a big part of the problem is that you'd never meet him anywhere. He has expressed fears, verging on paranoia, that strangers will throw things at him, scream and mock him, or sic dogs on him. So he spends all of his time skulking around or holed up in his stinky fire trap of a room, avoiding other people to the greatest possible extent. He even hides from his mom and resents it when she encourages him to participate in the household.
Whatever social skills he gained at school have long since atrophied through neglect. On the rare occasions when he ventures out, other people probably do look askance at his eccentric appearance and behavior, only reinforcing his paranoia. Due to his limited self-insight, he still sees himself as a boy genius when he's long since become a creepy old shut-in.
As his mother ages out of her caregiving role and begins to require care herself, it's hard to imagine a particularly bright future lies ahead for old Clem.