He uses the word “méchante”, which means bad, also mean of course, but for the storytelling of the song, I interpreted what he said at Tours, and maybe also in some other venues, that you can be expressive with a song telling about the very sad moment when one lover, in this case not Mika, says I need to leave you now. The badness is in the fact that you remember to the person of the title that: ok now we are together, but I want to tell everybody how much you hurt me when I saw that sad smile in your face. Sort of posthume love revenge, in that sense he feels bad, but he underlines too that a real love song must be cruel.