1) The eyes
2) The teeth
3) The hand gesture
4) The fact that he draws the Uglydolls. As pictured Babo draws Uglydolls
5) David is a lefty, notice where the chopsticks are. Babo is a righty. Hmm. That's not helping my theory, is it? Sun-min is probably a righty though. Maybe it's to throw us off.
6) Babo has a little part in the head, David has a part in the hair.
7) Babo likes cookies. David likes cookies.
8) Babo means stupid or idiot in Korean. David is self deprecating, hence the name Uglydolls.
9) Babo is one of the earliest Uglydolls. I think it might have been the first.