To spread jam, butter, honey, etc. on a piece of bread (une tartine).
This verb can also be used in a figurative way to convey the meaning that someone is putting a lot of something on top of something else.
No need to tartiner your face with make-up. Nothing can cover that massive pimple!
Worth being taken out in public.
He isn’t sortable! Every time we eat at the restaurant, he picks his teeth with the tip of his knife in the middle of supper.