I've done some searching but still can't fully understand this sentence. Can somebody explain to me?
A cut is slang for a song, as in a cut off an album. A deep cut is a lesser-known song, one that devoted fans may be familiar with, but average fans might not. In the photo, the dude on the left is dressed up as Will Smith, in a costume seen in an episode of Fresh Prince of Bellaire. Here is a seen from that episode: https://www.youtube.com/watch?v=adwT8ZY-XHM.
@DanBron in the comments posted:
That’s Will Smith in the middle, and actor who rose to fame in a 90s/00s sitcom “Fresh Prince of Bel-Air”.
Both the fans are dressed up as his character from that show. The guy on the right in the hat with the camera is dressed up as the kind of instantly-recognizable iconic version of the character from the weekly musical intro. The guy on the left is dressed more obscurely from this scene. That image has become a meme, so the slang “deep cut” must mean either “obscure reference” or “sharp insult”. Unsure which
I have some friends who speak a similar dialect of English to the one displayed in those comments, and I’ve heard “cut” used for many things, including “track on a record”, which I haven’t heard outside that language community. I’m pretty sure the guy means “obscure reference” (the insult theory is possible but not as credible in this situation, because dressing up as a character, even a meme’d one, reflects enjoyment of that character).
Sometimes it will mean he went very far. For example, say your teacher gives you a project, with specific instructions, but you, you go for the deep cut and add in a couple more things that will make your project better. Your teacher might say, "Wow! You went for the deep cut!", as in "Wow! You went very far".