This is an incredibly popular french phrase which has been as over used as the word "fleek". It means 'do you want to sleep with me tonight?' If you still don't understand this I'll break it down into normal english. 'Trynna smash?'
Sup girl! Voulez vous coucher avec moi ce soir? I would but i'd actually rather shove my head down a toilet.
French for Do you want to sleep with me tonight?
Alex: Jenny, Voulez-vous coucher avec moi?
Jenny: non (no)