The incident happened after Thomas missed a putt in the third round of the Champions Guard Championship in Hawaii.
“I am an adult. I am an adult. I have absolutely no reason to say that.
“It’s too bad. I’m very embarrassed. This is not my kind of person. But unfortunately I did it. I have to stick to it. I apologize for that.
Thomas added: “I apologize to everyone and the people I offended, so I will get better.”
The PGA Tour said in an AFP statement: “As he said after the round, we agree that Justin’s comments are unacceptable.”
Entering the final round on Sunday, Thomas was tied for fifth place, four shots behind the co-leaders Harris English and Ryan Palmer.