Marshall: Why do you have to look good all the time?
Barney: Marshall, let me tell you a little story about something that happened a couple months back.
[flashback to Barney asleep in bed. The door bell rings, he instantly wakes up and gets out of bed in his suit pajamas. He answers the door to two scantily clad women]
Woman #1: We were just having a "Who's hornier" contest and we spilled massage oil all over ourselves.
Woman #2: Nice pajamas.
Woman #1: Can we use your shower?
[present:]
Ted: That's not a memory. That's from a porn movie.
Lily: Not just any movie. That's the exact scene from... Never mind.
Barney: The point is it could happen. And if it did, and I didn't look my absolute best for those greasy sluts, I'd regret it forever.