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Colton Underwood says somebody touched him inappropriately at his charity event in San Diego and, as a result, he cut his appearance short and got the hell outta there.

The current 'Bachelor' star explained on social media why he left his Legacy Foundation Garden Party early ... saying, "I was grabbed and touched inappropriately while people were throwing cameras in my face." Colton doesn't name the person who got handsy.

We have tons of video and photos from the event, and from all we can see ... Colton seemed to be enjoying mingling with his fans. There is NO evidence in these images of anyone groping him.

Although he's clearly upset about how the night ended, Colton still apologized to all the fans he didn't get to meet due to his early departure. As he put it, he "had to do what was best for me as a human being. I didn't sign up to be a piece of meat or a zoo animal."

'Bachelor' alums like Becca Kufrin, Garrett Yrigoyen, Blake Horstmann and Tanner Tolbert all showed up for the event.