Yes, I have a theory but it's kinda dumb
So in the game Dusttale in the Core or laboratory you can find 4 tapes. In the first one is Sans and Toriel talking, the last line that Sans says is
" folks, ill be here all night "
Let's hop into Deltarune now, when meeting Sans he'll say something like
" I already 'Befriended ' your mom last night "
Many think that Sans had sexual interactions with Toriel in Deltarune, but the sweet spot many people missed is right here
" folks, I'll be here all night"
" I already befriended your mom last night "
So, when Sans saying the Dusttale line he was referring that he's gonna stay with Toriel the whole night and well, fuck her.
If Frisk DID continue the pacifist Dusttale, everyone would've gotten to the surface happy and Sans would've said the Deltarune line
Long story short
Sans dusttale fucked my mom
