Fubblegum

Fubblegum is the het ship between Finn and Princess Bubblegum from the Adventure Time fandom.

Canon
When Princess Bubblegum was physically 13 in "Too Young", she had feelings toward Finn. However, she didn't seem to like Finn in any other episodes. and sometimes she even feel awkward about Finn's attempt to pursue her. In "The Pajama War", Princess Bubblegum was hanging out with Finn. In series finale "Come Along with Me", Princess Bubblegum kissed Finn, but not romantically. After the main series, Bubblegum is living with Marceline, and Finn and Huntress Wizard are still keeping in touch, as seen in "Fionna and Cake".

Fanon
Fubblegum was very popular in the early seasons of the series. However, sometime after "What was Missing", the popularity of Bubbline surpassed Fubblegum. One of the reasons why people don't like Fubblegum is the age gap between two characters, since Princess Bubblegum is way older than Finn.

Trivia

 * Princess Bubblegum actually kissed Finn more than she kissed Marceline on screen. In total, Princess Bubblegum kissed Finn 4 times ("Too Young", "Wizard Battle", "The Real You" and "Come Along with Me") on screen, while she only kissed Marceline 3 times (one time in "Come Along with Me, 2 times in "Obsidian") on screen.