What is it about Tina Fey that makes her so funny? Is it the art of her awkwardness as Liz Lemon on 30 Rock? The silliness of her Weekend Update style on SNL? Or the dozens of LOL-worthy quips from her most recent writing and acting project, Unbreakable Kimmy Schmidt? Or is it that she just nails every single one-liner in all of her roles ever?Whatever the case, it's undeniable that Fey has mastered the whip-fast execution of smart humour.Fey turns 46 on 18th May and we're pretty sure that she just keeps getting funnier every year. She started out in comedy as a writer and improv comedian. After moving from Chicago to New York to write for SNL with the esteemed Lorne Michaels, she became the first female head writer at the show. Under her "regime" (as Janeane Garofalo called it in the New Yorker profile of Fey), the show underwent a major facelift, transitioning from a testosterone-fuelled clubhouse to a balanced, yet still tastefully crude, sketch show that continues to win Emmys and Writers Guild Awards.Beyond the writing gigs, Fey shines most when delivering her quick hits. And in good comedy, one well-delivered line is often all it takes to get the big laughs. Here are her 12 best.