Basically, UFC stands for Universal Fighting Championship, and is comprised of many different types of martial arts, so you can't "learn" UFC. Karate is basic self-defense, which can help relatively quickly, and ninjitsu is a misspelling of ninjutsu and jujitsu. The former is more guerilla warfare tactics, which would not be practical for dealing with a bully in short-term. Jujitsu is about using your opponent's power against him, and would be best for dealing with a larger, slower enemy. You decide which is best.
(Troll?)