The Three Days Rule
How I Met Your Mother Season 4 Episode 21 (04/27/09)
The episode opens with Ted getting the number of a beautiful girl Holli (Rebecca Budig). Barney convinces Ted he needs to wait three days to call Holli.. because of the rule originated by Jesus, of course. Ted gets home that night and decides to text her instead, he only said he'd never call her! After spending two days texting the girl, we find out through Robin that it's actually Marshall and Barney texting Ted. They were trying to protect him by pulling a Ted and telling Holli he loved her too early (like he did with Robin). They pulled it off by swapping Holli's number for Barney's work cell number in Ted's phone. They also use the help of an uber-romantic guy, Stan, who even gets his own theme song as he utters sweet nothings.
After Robin tells Ted, he gets his revenge by texting back that he had a sex dream about his best friend the night before. Ted instead decides to head off to where Holli's works and ask her out on a date. Turns out she was actually crazy and the date went horrible. The episode ends with Robin going on a date with Stan.. the guys' mancrush.