Brick Joke: with a Trailers Always Spoil subversion. The trailer spoils Harmony severing Harry's finger with a door slam. However, this doesn't happen until their second conversation at her door. The first time through the movie, viewers anticipating the joke might dismiss it as a Missing Trailer Scene... Until it sneaks up 20 minutes later.
Harsher in Hindsight: an in-movie example. The prologue featuring the young Harmony play-acting during Harry's magic trick ends with who we can only assume is her father about to smack her, then credits roll. Framed humorously, it foreshadows the fact that Harmony's father was a tad physically abusive, to say the least.
Hilarious in Hindsight: Two of the books on Harlan Dexter's shelf, seen while Harmony browses through his collection of Johnny Gossamer books, include The Lonely Black Widow and Thor. Two of Robert Downey Jr.'s co-stars in The Avengers play characters with these names.
Ho Yay - Perry/Harry, complete with a fake kiss between the two. Plus, the ending sees Perry and Harry working together, while Harmony is noticeably absent. In an earlier draft the film ended on a scene and end-credits voiceover between Harry and Harmony; in the final film, both of those have been excised in favor of not just one but two scenes between Harry and Perry.
Pandering to the Base: The ending has Perry finding Harmony's elderly father, before he strikes him twice for being a monster. Those who don't find it satisfying even get a comment from Harry, who comments on how brutal it is.