I have been experimenting with different masturbaton technics over the years. My favorite by far is 'exercising' in the shower.
I have over the years collected many 'toys' of different sizes and shapes.
My favorite is to turn on a warm shower 20 or 30 minutes before my girlfriend turns in for bed. I get in the shower with my favorite 'toy' (a very large one), some lube and a soft pink masturbation sleave. I start by soaping my body up and rubbing myself all over then wash off. Then I lube my cock and ass up and then squat on the 'toy', inserting it all the way. By this time my cock is rock hard and I start going up and down on the 'toy'. I hold off until my girlfriend comes into the bathroom and 'catches' me using the 'toy' on my ass. It excites me so much being caught that I usually cum with in 5 minutes of her standing there watching me enjoying the 'toy'. I shoot my cum into my hand and lick it off while she watches.