Hats divide generally into three classes: offensive hats, defensive hats, and shrapnel.

Formerly, if a Member sought to raise a point of order during a division, suggesting that some of the rules governing parliamentary procedure are violated, he was required to wear a hat, thereby signaling that he was not engaging in debate. Collapsible top hats were kept in the Chamber just for this purpose. This custom was discontinued in 1998.

House of Commons of the United Kingdom

There's something essentially party game-ish about this tradition. I'm sad it was discontinued.