for the first time I will have a hard time deciding because there's more than one, a lot of her singles are beyond overrated. We have Bad Romance, Poker Face, Just Dance and Born This Way as being the most overrated singles by her.
I will exclude Just Dance and Poker Face because I remember I really liked her back then and she used to be pretty and not overrated as an artist. So we have Bad Romance (although is a copy of Poker Face sounds a little better and blew my mind when it came out but right now I see it as being overrated) and we have Born This Way (that is a copy of Express Yourself and has nothing to be a hit and was).
Okay this was enough, now I don't have doubts, although Bad Romance was in fact overrated, it has some very catchy stuff about it and it actually deserved to be a hit, people just "ruined" it for me, but Born This Way seriously, just no, I still don't like that song that much.
BORN THIS WAY
at the people who said Judas (which flopped hard 
)