I have one now for three different shows I like to watch; Friends, The Office, and now How I Met Your Mother. I pulled it off the internet but have made some of my own modifications.
How I Met Your Mother Drinking Game
Anyone says "Awesome!"
Anyone says "Bro" or "Bro-something"
Robin says "literally"
Barney says "legendary"
Barney uses a pickup line
Barney says "Suit up"
Lily talks about or is around her kindergartners
Anyone says "Have you met..."
Barney does magic
Anyone does a high five
Barney says "Ha, please."
Barney says "Daddy's home"
Marshall says "Lawyered!"
Ted does a voiceover
There is a flashback
Barney says "What up?"
Barney mentions his blog
Marshall sings about what he's doing
Barney calls himself Ted's best friend
Ted says "How I Met Your Mother"
Any mention of a slap bet
Ted makes a Star Wars reference