His Favorite Is Luke Skywalker

Why makes this Joke funny?

The humor in the joke:

"My friend decided to get a face tattoo of his favorite Star Wars character.
You should`ve seen the Luke on his face!"

lies in the play on words, specifically a pun, which is a form of wordplay that exploits multiple meanings of a term, or of similar-sounding words, for an intended humorous or rhetorical effect.

The joke hinges on the double meaning of the word "Luke," which refers to both:

1. Luke Skywalker, a central character in the Star Wars franchise, presumably the character that the friend got tattooed on his face.
2. "Look," which is phonetically similar to "Luke" and is part of the common expression "You should`ve seen the look on his face!" This expression is typically used to indicate that someone had a noticeable and often humorous or exaggerated reaction to something.

By substituting "look" with "Luke," the joke connects the expression on the friend`s face to the face tattoo of Luke Skywalker in a clever and humorous way. The punchline plays on the anticipation of hearing about the friend`s reaction (the "look" on his face), but instead delivers a pun that ties back to the setup about the Star Wars tattoo, creating a humorous and unexpected twist.