BUSTY AUTOGRAPH

Justin Thomas got REALLY close with one of his biggest admirers at the Valspar Championship over the weekend ... when he signed a female fan's boob -- and it was all caught on video!!!

The hilarious moment went down as social media influencer/OnlyFans model Karin Hart attended the event in Florida ... when she explained on her Instagram story she wanted the two-time major championship winner to autograph her chest.

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