Take the muffler off of your car, or if not rev it up loudly. The neighbors will hate you for the excessive noise, but you will feel "cool".
Let your pants creep down in the back so that people can see your "cool" crack.
Use the "F" word in at least half of your conversation. People will be amazed at the level of your vocabulary skills.
Bop up-and-down as you walk. This should make you THINK you are cool.
Wear your cap/hat backwards, with the 'visor' behind your head.
Spit on the ground constantly.
Wear excessive jewelry. Enough to make you THINK you are cool.
Wear a metal-studded black jacket with totally senseless pictures and words.
Be completely fake. Do not show your true "un-cool" self.
Wear a walk-man all the time. You may THNIK you are cool in this anti-social state.
Brag to other people about how smart you are (in your own mind).
Blast your music near those who don't want to hear it, even when you have earbuds in your pocket. You will feel 'cool'.
Drop/smash your weights at the gym on purpose. You may THINK you are cool for doing it.
Brag about your time in jail or prison, and of your criminal offences.
Brag about your parent's wealth and success. People will despise you, out of jealousy, but YOU may feel satisfied as you put yourself above others.