For the high jump

Quick question.

Some friends were recently invited to a fancy dress party with the theme of ‘sport’, and while discussing how odd this was we quickly ended up competing over who could come up with the most obscure/tangential costume. After a while I said:

Just turn up in normal clothes. When people ask why, say ‘well, I assumed if I didn’t put in any effort I’d be for the high jump’.

All right, so it’s not the best joke ever. Shut up. I mention it because I killed the conversational thread. Silence fell for a few seconds, and I was swiftly informed that nobody at the table had any idea what I was talking about.

I tried the same line the next day with some slightly older people, and they thought it was funny. All right, maybe not ‘funny’, but they understood what I was trying to do. I got pitied, which I call a result.

So: quick straw poll. Who understands the phrase ‘for the high jump’, and roughly how old are you?