Dubious entry, for a dubious practice. We would all go in the boys bathroom at primary school (girls may have practised this... though it seems unliikely). Whoever felt brave would sit on the floor with their back to the wall, hold their breath for 30 seconds, close their eyes, and cross their arms over their chest, while tucking their knees up to their chest. At this point 3 or 4 remaining boys would push his chest (with shoulders, arms) as hard as they could for a 10 seconds or so. Lack of blood (and oxygen) to the brain was the result. Unconsciousness of the individual ensued.

Variants involved using the stone wall in the playground, and an excess of 6 or more people pushing on ones chest. This nameless act was swiftly outlawed, in fear of widespread braindamage. It was none-the-less the best thing we 10 year olds ever did. Apologies if it has been posted under another name. Or if any of the kids from this Nottinghamshire primary school are permanently damaged...