EXCLUSIVE

Colton Underwood's penis and virginity came under fire during his charity event in San Diego, leaving the 'Bachelor' star feeling deeply disturbed and violated.

Eyewitnesses tell TMZ ... during Colton's meet and greet, a female fan approached him and grabbed his crotch in front of everyone, telling him, "I am going to take your virginity."

As we reported ... Colton cut his appearance short and got the hell out of Dodge before apologizing to his fans for his early exit, saying he was touched inappropriately.

Sources close to Colton tell us he needed a moment to compose himself after he was groped, so he stepped away into a VIP area, but then decided he'd had enough and left early. We're told he feels bad about leaving his fans hanging, but he just couldn't go on.

As you know, Colton's virginity has become an endless punchline on "The Bachelor" ... but after Wednesday's encounter, we're told Colton feels the virgin jokes have finally crossed the line.

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