Usage notes: The French expression ce n’est pas mardi gras aujourd’hui is used to tease someone who is wearing something ridiculous. Mardi Gras is famous for crazy costumes and elaborate masks – pretty much the more flamboyant, the better. But on any other day of the year, wearing something outrageous is likely to be mocked.
Élise, qu’est-ce que tu portes ? Ce n’est pas mardi gras aujourd’hui !
Élise, what on earth are you wearing? You look ridiculous!
Related expression:se croire à mardi gras – literally “to believe oneself (to be) at Mardi Gras”
Il se croit à mardi gras.
He’s dressed as if she’s at Mardi Gras, He looks ridiculous.