Flowey actually enjoys music, and singing, even when he's SOULESS, but doesn't sing often, because he thinks that other people would hate it, "Frisk" almost killing him, and telling him to shut up, only made him more definate on that thought.

Flowey is afraid of RESETS. 

Flowey loves Telltale games, because you can't go back on the choices you make.

Flowey is actually fond of (The real) Gaster, thinking of him kind of like a father figure.

One of Flowey's worst fears, is being trapped, which is why he hates being in a pot so much.

Flowey loves drawing and writing stories, but doesn't because of his lack of arms. It's difficult to write with your mouth.

Flowey is pansexual.

Flowey despises HUMANS, more than he despises RESETS.

Flowey is allergic to olives.

Flowey HATES any form of discrimination or racism. Making him defend others in those types of situations. 

Flowey absolutely, positively loves Christmas!

Since Flowey doesn't have any real friends, other than Ava, he usually listens to other people's conversations, which gives him an advantage when it comes to presents or gifts, making him great on birthdays or holidays

Flowey likes clowns.