A guy who has success in having sex with lot of girls. A P.B. is a guy who doesn't waste time trying seducing a girl. He needs only to look the girl and say few words to get laid with her. A P.B. hasn't a girlfriend, but he has got lots of female friends with whom having sex when he wants.
When in a race (normally from a roll) The operator of a "boosted" (turbocharged) car does a tricky maneuver involving applying brakes then adding in throttle to add more brake smoothly to eventually cause the engine to load up spooling the turbine creating boost/power while maintaining a constant rpm/speed so that when the driver lets off the brakes the car takes off like a bullet.
The car on the left brake boosted on that race.... didn't you hear the turbo spooling before they went?