A punch to the heart that doesn't have to hurt you physically but damn sure goes straight to the feels.
"Fuck you Kenny, you can't go studying abroad! You are the worst best friend ever"
*SMACK*
"That didn't even hurt"
"I don't care, it was a soul slap!"
Despite the somewhat misleading name a nanocunt is someone who is being a cunt of biblical proportions.
Omg Chris you drunken foofer! Stop being such a nanocunt and go home!