Sharing is fine and good if it’s French fries, bad advice or the warmth of a fire. But with girlfriends, cigars and motorcycles, no. That’s biker law. Complicating this situation is that if one of us ever did, on his own, decide to offer our bike up for someone to ride, it wouldn’t be to someone who’d asked if he could ride it. That’s an age-old biker rule, too: Having asked automatically excludes a person from ever being considered to ride your bike. That’s because having asked guarantees bad manners all around. Off he’d go, launching into a wobbling wheelie, returning in a sliding stop with the rear brake locked, capping off the ride by staring you in the eye with feigned innocence and a smile. If you’re lucky, he’ll give you this look while handing your bike back to you. If you’re not lucky, he’ll give you the look while sprawled on the pavement at your feet, your bike on top of him.