For me it was Tom Watson.
Growing up, there were two seasons. Hockey season, and golf season. And for me, there was no athlete that epitomised the excellence I sought in my own performances more than Jack Nicklaus. I idolized that guy. I loved that he basically told the PGA Tour that he didn't give a damn about the little tournaments, he wanted his career to be measured on the biggest stages, the Majors. And nobody dominated the Majors like Nicklaus until this Aw Shucks Schmuck from Kansas came along and bested Jack toe-to-toe at the British Open in 1977 and the US Open in 1982, when Jack was really in his late prime and striving for history. That drove me crazy with rage.
A few years later when Nicklaus was done with competitive golf, I rejoiced when Watson got the yips and started consistently whiffing on 3 foot putts. I loved that.
Having said all that, I look back now at my youthful dislike for Tom Watson and I'm embarrassed. In his old age, and mine, I've softened on the man and can now finally respect what a great player and man he is.
So which current or past athlete do you dislike the most?