I like to go very slow, because it's the ultimate tease.

And speaking of teasing, if you really want to make a man lose the ability to reason, I recommend the following. After a relaxing evening of fun, do something nice to help him relax. A massage or bath are to excellent ways to help him leave his responsibilities behind. Starting at his lips, kiss him slowly and deeply. Then slowly work your way down his body, stopping at all his favorite spots along the way. Don't forget to tease his nipples, brush your lips gently along his skin and tickle him with your hair. Give him great oral sex, and when he's nice and hard, switch to analingus. Slide you tongue inside and out, and after he's accustomed to having your wet little tongue in there put a little lube on your index finger and explore with it. Take your toy, put lube on the tip and slowly slide it inside. Then turn the vibration on low. As he sighs, leave your left hand on the toy and switch back to giving him head or a hand job, while the vibrator is still on. As he warms up to the situation, you can fuck him with the vibrator and your mouth at the same time. Scientifically speaking, stimulating his prostate and cock at the same time will make him cum really hard and turn him into protoplasmic mush.