Mitar is a slang that came about thanks to the internet and that means if turn it into a myth or do something in an exemplary way.
This word does not appear in the Portuguese language dictionary, because it is a neologism, a word created from the noun myth.
Learn more about meaning of myth.
On social networks like Facebook, it is said that a user "mythed" when he made a very funny comment, which had many likes. On many Facebook pages, when a post is made, users try to make a mythical comment, that is, funny, sly and/or clever. When they do, they receive several likes and it is recognized that they "mitt". In some cases, the comment is so popular that it gets more likes than the original post itself.
See also:meaning of mitou.
It can have a similar meaning to ownar, or to perform a task in an expert way. Ex: My team's striker scored 4 goals in the match! / I did it with my last Facebook comment, I got over a thousand likes!