Directions: pull over and ask a passerby for directions in a hurried, panicked voice. Wait for them to start talking before looking over your shoulder, shouting "shit they're onto us" and driving off rapidly. You'll leave them mightily confused and looking around for the police (or possibly the mafia).
This game went very wrong when we asked this one guy for directions to the A14 from Robinson College. Not only did he gave us completely wrong directions, he repeatedly told us that he only had one arm, and then demanded money for his disability and for giving us (useless) directions. We drove off pretty quickly.
Trailing: find a car, pretend to be a gangster and trail it around town until the driver gets nervous. It's super effective if you switch your lights off. We made the mistake of following a BMW with blacked-out windows, and it was only when he started to double up his route and take us down one-way streets with no escape routes that we got worried and realised that he actually could be a gangster. Again, we drove off pretty quickly.
Adverse Camber: this game relies on the fact that a lot of people aren't entirely sure what an adverse camber is. Find a stretch of roads with an adverse camber (we used a bridge with roadworks) and, as you drive across it, frantically warn passing cyclists and pedestrians to watch out for the adverse camber - "be careful mate, watch out, there's an adverse camber ahead!". If they don't look worried or confused enough, all lean to one side of the car to emphasise the point.
The Yes/No Game: this one's simple. Wind the windows down and drive around rating members of the other sex. It's especially amusing when you come across, say, a group of 5 girls, and Rob leans out the window and picks them off individually: "No... NOOOO.... She's a definite Yes.... You at the back, NO .... Yes!" The game can be spiced up by rating out of 10, rather than just a simple yes/no.
Don't make the same mistake as Dingly, who insulted a cyclist just before we pulled up to a red light. Cue the hilarious image of him frantically trying to hide under his seat and wind his window up as the cyclist approached.
Official Race Car Game: Find a jogger, put your hazard lights on, slow down and shout motivational slogans at them: be their official race car. Ian and Rob accompanied Horrocks (down Burrell's walk!) in Romsey 3.