He doesn't like you. I don't like you either. You had just better watch yourself.
This is one of my all time favorite scenes in ANH. Dr. Evazan and Ponda Baba picked a fight with Luke only to get their asses kicked by Ben Kenobi. Luke unintentionally brought this upon himself. Watch as he enters the cantina. You see his lightsaber openly hanging from his belt. He didn't try to conceal it like Ben (and the other Jedi) always do. Luke should've known better. Lightsabers are illegal for anyone except a Jedi (or a Sith) to carry and at the time, just being a Jedi was illegal. Dr. Evanzan and Ponda Baba probably thought Luke was a Jedi (wannabe). They were also intoxicated, which didn't help either.