The Pact/Bet
In honor of the fact that the wife of Michael B. Jordan's character Mikey wants a divorce, the three guys make a pact to remain single. See also: So many rom coms have pacts or bets that shape their plots: How to Lose a Guy in 10 Days, the recently-anniversaried She's All That, and 10 Things I Hate About You. This trope is a fairly classic one, going at least all the way back to Shakespeare's Love's Labour's Lost.
The Meet Cute
Jason meets Imogen Poots' Ellie in a bar as she is rejecting advances from another guy. Other guy asks to buy her a drink, and she starts ranting about the rest of their lives together. Jason joins in with a quip about how she and random dude would go to the lame Hamptons. It's banter! Sweet, sweet banter, and it means they're made for each other. See also: every rom com ever.
The One-Night Stand That Isn't
Jason and Ellie sleep together, but he mistakes her for a hipster hooker and sneaks out. The next day, she shows up at his office. See also: It's TV and not movies, but this is how Grey's Anatomy starts. In Working Girl Melanie Griffith's character meets Harrison Ford's at a party, passes out thanks to alcohol and Valium, and wakes up in his bed. They didn't sleep together, but the next day, she finds out he was the person with whom she had previously set up a meeting.
The Break-In
Jason and Ellie pilfer a key to Gramercy Park and break in. See also: Hugh Grant and Julia Roberts breaking into a garden in Notting Hill; or Kat Dennings and Michael Cera going to the recording studio after-hours in Nick and Nora's Infinite Playlist.
The Embarrassing Costume
Jason, mistaking "dress-up party" for "costume party," shows up at a birthday party Ellie is throwing for herself in a "Rock Out With Your Cock Out" costume. (He has a large dildo hanging from his pants.) Ellie's parents are there. See also: Reese Witherspoon's Elle Woods attending a party in a Playboy Bunny costume in Legally Blonde, also Renée Zellweger's Bridget Jones in basically the same costume in Bridget Jones's Diary.
The Best Friends Who Fall in Love
Chelsea (played by MacKenzie Davis) acts as the wing-woman for Teller's Daniel, until he brings pizza over to her apartment one night and they realize they are perfect for one another. See also: The mother of all friends who fall in love rom coms, When Harry Met Sally, also the friends-who-fuck duos of Friends with Benefits and No Strings Attached.
The Caught-In-The-Act Sex
Chelsea and Daniel try to have sex in a bathroom shower at Thanksgiving but are caught by Jordan's Mikey and Jason. See also: Not exactly the same, but in Four Weddings and a Funeral, Hugh Grant's character is accidentally in a room when his just-married friends escape to do it. Also Jake Gyllenhaal and Anne Hathaway were caught in the act by Josh Gad in Love and Other Drugs.