Masturbate. I'm serious. That's the best stress reliever ever, if we're not talking about a very good sex, that is.
But if you're not into that kind of thing—yet, or ever—you can just sing to your heart's content.
But if you don't live alone and your walls aren't that soundproofed, you can just sit back, relax, and escape into good stories—novels, anime, manga, manwha, movies, TV shows, it doesn't matter.
If that still doesn't do it, maybe order your favorite food or snack and really take your time savoring it.
Oh, almost forgot. Another best way to relieve stress is to talk with someone, especially someone you trust and has a good connection with, someone with a good vibe.
You can also take a healthy approach by exercising and going to bed after having been fully spent.