Littlefinger betrays Ned (Episode 7, "You Win or You Die")
"I did warn you not to trust me," says royal beancounter, proud pimp, and would-be romantic rival Lord Petyr "Littlefinger" Baelish as he holds a knife to Eddard Stark's throat. Okay, so that's one thing dude's been honest about. But after spending the season leading Ned from clue to clue in his investigation of the death of the last Hand of the King, then offering to buy the support of the City Watch for Ned's coup against newly crowned King Joffrey and his mother Queen Cersei, the one-time confidante of Ned's wife Catelyn revealed his true colors, betraying Stark and slaughtering his entire fighting force in a single move. For that, Littlefinger gets the longfinger.