(you're playing through undertale on genocide, and that means you have killed all sans's friend including toriel and papyrus, so you finally got to sans and it was your 21st attempt of you are trying the hardest to win, but He keeps laughing at you)

Sans: hahaha you just need to give up kid, you can't defeat me, because I'm stronger than you, remember, I said it again and again but you won't listen (He says it with a teasing grin)