Madison Keys' fiancé found himself in a pick-le ... 'cause ESPN jumped to him at the wrong time -- and, they caught him fingertip deep in his nostril.
The American tennis star was in the third set of her round of 16 match against Italian player Jasmine Paolini Sunday when ESPN's broadcast flashed over to her coach and fiancé, Bjorn Fratangelo.
Check out the clip ... Bjorn's hanging out and chatting with a woman to his right, when he brings his fingers up to his nose and decides to drag out a bothersome boogie.