When you accidentally f**k your girl while her tampon is still in her pussy, thereby pushing it deep into her vagina. When you finish intercourse, you have to retrieve the tampon and "fish it" out of her vagina.
Guy (while fingering his girl after sex): "Uhh, I feel somethin' fuzzy in there"
Girl: "Oh sh*t, that's my tampon, can you get it out?"
Guy (to friend): "had to go tampon fishing last night...f**k man, never again."