interjection/a d‿otʁ/
don't give me that! tell it to the marines! my eye! pull the other one!
Synonyms: mon œil !, mais bien sûr !, c'est cela !, laisse-moi rire !
See the phrase on ne me la fait pas (“bullshit won't work on me; I'm no sucker, I'm no fool”); perhaps an ellipsis of something such as fais-la à d'autres (“try it on someone else”).