Lily tries to comfort Barney who is enraged at the idea of Ted and Robin sleeping together again. Lily tries to get Barney to admit he still has feelings for Robin.
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In this clip from the the upcoming episode of How I Met Your Mother, Robin and Ted are driving each other nuts as roommates. They think maybe have sex will solve the problem... much like Barney thinks it will solve world peace.
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In this scene from "Little Minnesota," Ted thinks his sister slept with Barney and he decides to confront her on it. A great reaction from both her and Barney.
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HIMYM Quotes

Barney: Ladies and gentlemen, I have in my hand a copy of tonight's Top Ten list. The category: top ten things I would've called my truck...
Ted: It was never your truck.
Barney: if Ted hadn't been a jerk and given it back.
Ted: It was a rental.
Barney: Number ten, "The Winne-Bango." Number nine, "The Pick-Up Truck." Number eight, "The Ford Explore Her." Number seven, "The You Scream Truck." You Scream. (they all laugh) Number six, "Feels on Wheels!" Hello! Number five, "The Ride Her Truck." Number four, "The 18-Squeeler." Number three, "The Esca-Laid." Number two, "The Slam-Boney." and... the number one thing I would've called my truck if Ted hadn't been a jerk and given it back... "The '69 Chevy."

Sometimes things have to fall apart to make way for better things...we're done here.

Ted