Love Montage

Absolutely this.

When a new romantic relationship has been formed between two characters in a movie or TV show. There may be a pop song about love playing in the background as the two go through various scenes expressing their love for each other. If anything goes wrong during these scenes, they're either easily fixed or simply laughed off by the playing characters as nothing can actually go wrong during this UnTrash's playing. In times of a romantic New v Old plot, the "replaced" partner will miserably watch from a distance as their loved one is swept off their feet time and time again by the Newcomer, Throwing Salt On The Wound in the process.

This UnTrash has the reputation of being so overplayed and eyeroll-worthy that there have been numerous efforts to parody it, even entire movies and episodes of TV shows made for the sole purpose of spitting in the face of the disgustingly overplayed romance UnTrashes of fiction, including and especially Love Montages. Some of those efforts were very successful.

Love Montage might be played when two bad guys get together, fall in "love", and hit the town by doing more evil, this time as a team, although this is rarer than a basic Love Montage.