When you or someone else insults someone in their head
Can be used while also saying something nice outloud
Timmy: Hey buddy I got the iphone 6+
Tommy: (thinking) why don't you shut the fuck up u faggot I'm bout to slap the tiny dick off you
Tommy: (saying) oh that's cool Timmy
Timmy: (thinking) the fuck did u just mental insult me u retarded meatball