For those who are breast nipple sensitive: Undress and take a chord, flexible and a little rough, 3 mm in diameter. I use the nylon one I purchased in a trekking equipment shop. Lead it under your penis between the glands and the foreskin pulled back. Lead the end of the chord coming from the right side of your best friend to the left breast nipple and the other end to the right nipple upwards. Make short movements with your hands holding the chord up and down by touching the nipples with the chord or tips of your fingers. You are stimulated on three points at the same rhythm! You can change the speed, pressure and produce any sensations you like.
There is one trick you will find inevitable. As you approach orgasm, your penis will stand more upright and the chord could slip out of its place and you will have to finish manually. In order to enjoy extreme pleasure, however, you must prevent the slippage: load your penis previously by hanging a weight on it just behind the chord. (I take two alpine climber's clips for the purpose.) So the weight pulls downwards, the cord upwards-and the tiny zone of your penis, sensible like a feminine clitoris, will drive you inevitably towards the culmination.