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.
instagram.com/p/Cp8o5w5MdQ9
Hart's big opportunity came about an hour later when JT was signing items for fans ... and she pleaded with the golf star to fulfill her wish.