A company is selling printer paper that can be used to make temporary tattoos. You just Photoshop yourself a wicked skull and crossbones or unicorn, and you're good to go.
Once it's printed you just need to apply an adhesive sheet to the printout and smooth out any bubbles. When you remove the adhesive sheet, the printed tattoo will be left with a sticky surface allowing it to be applied to your skin with a wet sponge. The tattoos are water-based and non-toxic, so while they'll stick around for about a week if you avoid bathing or showering, they can easily be removed with just soap and water.
Each sheet costs $5. While this is pretty neat for kids under the age of 10, if you want to earn real street cred you need to do what I did: Get in a bar fight and kill some dude with a highball glass. Then make sure to be represented in court by a public defendant so you're guaranteed a max sentence. While you're in prison kill somebody else (go for someone small) and get your cellmate to tattoo a blue tear under your eye using a sharpened spork from the cafeteria. Presto -- when you're out of the slammer everyone knows you killed somebody. Sure you may lose your virginity in the communal shower, but hey, it's all part of the experience.