Here's where we can scream about how much we hate Frans/Fontcest.
AKA the two baddest ships in the fandom.
Frans is the ship name for Sans x Frisk. The reason it's bad is because..well, Frisk is a child and Sans is presumably an adult. I'm pretty sure Toby confirmed Sans to be an adult and it said right in the trailer that Frisk is a child. So it's pedophilia. Aging up Frisk doesn't make it any better. It just makes it creepy.
Fontcest is the Sans x Papyrus ship. It's bad because they're brothers. Enough said.