The act of extreme masturbation. You must "bust one off" whilst sat in an airport bathroom after pulling the red emergency cord. The race is on to 'let the bubble see the pop' before security come investigating. Ejaculation must be reached before your Terminal Two Tug 'target' arrives to investigate. The greater the chances of being discovered going to town on oneself, or pulling one's war face is obviously where the danger comes from. The more danger involved the harder (or softer) it is to complete the task in hand (snigger). Saying originated in Swindon, UK after a spate of adventurous 'danger wanks' by one bar hostess became local legend.