The incident occurred after Thomas missed a pair putt during the third round of the Sentry Tournament of Champions in Hawaii.
“I’m an adult. I’m an old man. There’s no reason to tell me anything like that.
“It’s terrible. I’m extremely embarrassed. It’s not the kind of person I am … But unfortunately I did, I have to do it and I’m very apologetic.
“I apologize to everyone and anyone I have offended and I will be better for it,” Thomas added.
“As he expressed after his round, we agree that Justin’s comment was unacceptable,” the PGA Tour said in a statement according to AFP news agency, which added that Thomas is likely to be fined for conduct “improper of a professional.”
In the final round on Sunday, Thomas is tied for fifth, four shots from co-leaders Harris English and Ryan Palmer.