In Happy Tree Friends, all episodes featuring a romance end poorly for the couple. This is most notable with the Official Couple, Cuddles and Giggles, who have the most deaths in the series, and have not survived a single date...until I Nub You, where they were used as a Beta Couple for Petunia and Handy. The latter pair died horribly, but Cuddles and Giggles survived.
Any time Pop and Cub both live in the same episode.
In Party Animal, Flaky throws Flippy a surprise party. When presented with the cake, he cries a Single Tearof gratitude.
It's easy to miss, but Flippy's myspace page states that he loves chocolate chip cookies. When we see Flaky baking the cake, there is an enormous plate of chocolate chips among the ingredients. Cue Fridge Awwwww.
Also, in Without a Hitch, Flippy constantly wants to help her, despite her obvious avoidance.
Lifty and Shifty have a long history of cheating and stealing from everyone, but Lumpy in particular. So when he sees them go flying by in a runaway cart on his death trap of an amusement park ride, what does he do? Hop on a handcar, chase them all over the ride until he sees the end of the tracks looming, then grab onto a string of flags and flip overhead into their cart, pulling all three to a stop at the very last second. Their reaction cements the moment as a CMOH.
Lumpy's determination to save his pet elephant in Junk in the Trunk. It helps that this is one of the few aversion this series has of Shoot the Shaggy Dog.