Loboto? Totally Bobby's dad. Seriously.
Seriously. Lanky? Blue skin? twotone red/green eyes? Showercap possibly concealling afro? Antagonist to Raz, too!
Sure, Bobby didn't mention it, but for all we know Loboto knocked up his mother and left, also a good reason why the surnames are different. Plus, if your father had just taken out everyone's brains and revealled himself to be a loony, and you had a reputation to uphold, would YOU tell anyone it was your dad?!
Also, it leaves a good explanation of how Loboto was pushed into insanity...
...If you were a dentist and you had a kid with teeth like that, wouldn't you go insane too? I know I would.
Alternatively, Loboto messed up Bobby's teeth even more than they originally were.
But yeah, if there's ever a psychonauts sequel, they need to have a Star Wars moment between Bobby and Loboto. :D