Several things in 'Real Genius' point to Doc Holliday:
1. Chris puts a
coin in the vending machine, then holds a coffee cup that has
playing cards on it (the first time we see Doc in 'Tombstone' he has a coin on one hand and cards in the other).
2. Chris
rolls coins on his knuckles - it's our introduction to Doc Holliday. One time Chris does it with both hands while closing his eyes or not focusing, similar to Doc's "I have two guns" scene (meaning they don't have to see well to do something perfectly).
3. One of the T-shirts Chris wears in the movie is of
Roy Rogers in a
cowboy hat, and he wears it in a scene where he is helping a friend take
revenge on someone.
4. Chris says the line "What's up,
doc?"
5. Chris and the other students act
dentists when they use dental tools to plant a transceiver in Kent's mouth.