A pretext for a large group beating up someone weak, eg:

Birthday billies: Getting beaten up because it's your birthday. In practise, if you were the unpopular kid, it was your birthday every day, and the sone 'Happy Birthday' quickly became an infinitely greater torture than, say, having your scrotum burned by cigarettes while you are stretched by a rack.

Silent billies: Someone shouts "Silent billies 1 2 3!" and the first person to make the slightest noise gets beaten up. Could get tricky if a teacher asked someone to answer a question, as you faced a choice between disciplinary action from the teacher for being insolent or from the other kids for not being insolent.

Movement billies: Same as above, only someone shouts 'movement' instead of 'silent,' and the person beaten up is the first to move the slightest bit. Eyes, lungs, and hearts were generally (though not always) exempt. Here, it was extremely easy to get whoever you hated beaten up by claiming that they had moved. It did not matter whether you could see them or not - the fact that you said they moved poved that they did. Besides, if you claimed wrongly, they would likely make an actual movement as they protested their innocence.

Silent movement billies: A combination of silent billies and movement billies. The most feared test of endurance of all, since people had a tendency to laugh while trying to remain perfectly still and silent.