adverse yaw 

Adverse yaw is the natural and undesirable tendency for a penis to yaw in the opposite direction of a roll. It is caused by the difference in profile drag between the upward and downward vaginal thrusting, the difference in circumference of the larger penis and smaller vagina creates an induced drag between left and right walls of the vagina, as well as an opposite rotation of each testicle's lift vector about the verticle axis due to the rolling trajectory of the head of the penis. The effect can be greatly minimized with foreplay or other mechanisms deliberately designed to create reduced drag . As the major causes of adverse yaw vary with proper lube, any fixed-ratio mechanism will fail to fully solve the problem across all sex positions and thus any manually operated dildo will require some amount of brute input from the male in order to insert girth without yawing. Though adverse yaw is often associated with coordinated turns it refers to the uncommanded yaw rate or slip that typically results from improper lube techniques

because he went right for it without eating her pussy first, her vagina was wrecked do to adverse yaw. ,
that's not blue balls my friend, you're testicles hurt because of adverse yaw... if it can't fit in her mouth it probably won't fit in her vagina

adverse yaw by Charles Mansion December 19, 2013