She was jerking me off in the shower (not uncommon), but when I said 'Mistress may I please come', she said 'no', and continued. I fought as long as I could, then gasped 'Mistress, please stop, please I can't control it', she said 'yes, you will. You won't come.' But then I started to come.
She grabbed my cock and squeezed hard. She later said that She really enjoyed feeling my cock throb as I came, and it all backing up behind her iron grip. Meantime I was squeezing my PC muscle as hard as I could, trying to prevent orgasm. And failing.
She let go of my cock, and I pumped semen over her thigh a couple of times. Then she kissed me, and said "happy anniversary". Then she stroked my cock as though to milk the cum after an orgasm.
"You really need to practice those Kegel exercises." She said as we climbed out of the shower.