David McCarthy, 19, was attacked on the social media site after he snapped a picture of himself and cyclist Marcel Kittel - whilst the athlete was sitting on the roadside gasping for breath.
And the teenager seemed unrepentant about his callous move, captioning the picture: 'Kittel collapsed after the line today so instead of giving him a hand up I took a selfie.'
The cyclist had just won the Armagh to Dublin leg of the cycling race, and had collapsed on the road, exhausted after pushing himself so hard.
'I didn't mean it in a bad way,' said David, from County Cork, Ireland.
'I was standing on a post box 100 metres behind the line, I hopped off it and there was Kittel beside me.'
The teenager added that he was only next to the cyclist for about two seconds, and really doesn't think the exhausted athlete minded at all.
David has now been posted an apology message to Twitter because of the backlash.
In it he writes: 'To marcel kittel and all the people I have offended by taking the selfie I apologise. I did not think the photo would cause such hate towards me'.
He added that he had just got excited by seeing the German cyclist and made the wrong decision.
Marcel Kittel has been forced to pull out of the next part of the contest because he is suffering with a fever.