Ordinarily, I don't easily dislike any cyclist and it's because of the immense effort they all put in their career. But if I must choose one person who's my least favourite, it's going to be Pedro Delgado.
He was highly criticized for winning 1988 Tour de France amid doping allegations. To crown it all, he protected to avoid embarrassment for the event. Doping is one thing I don't easily overlook in any sports because that's wrong.