BOXER SHORTS RUB
MASTURBATION

DIFFICULTY =  Easy 
LUBRICATION = No

In this technique, rub the penis with your knuckle through the fabric of a comfortable pair of boxer shorts  or other underwear.
You can also get a better grip on the testicles with the other hand by using this method. As a variation, try 
it with a thicker fabric such as denim or jeans. This can prolong the intensity before orgasm.