A Johnson Outboard

This begins with the lady furiously masturbating her gentleman's penis. At the moment of ejaculation he performs a motorboat maneuver between his good lady's breasts (pushing the breasts together whilst shaking his face between them and slobbering), thus replicating pull starting a johnson outboard on a motorboat.

She had a rack to die for, so I bought her a drink and she gave me a Johnson outboard in the toilets.