A radiator knob occurs when a man lathers his gentleman fluid on a cold radiator then turns it on to full. He then invites his baby craving wife into the room who's urge for a baby is so great that she strips and try to catch the evaporating semen vapours with her minge hopefully not singeing her lips on the flaming hot radiator.
"oi love, you want a baby so bad? wrap your tuna tunnel round my radiator!"
"my husband left me after the radiator knob incident"