Whenever a system puts in that format I just change it back to AM/PM, I just don't like it, I like to have less numbers (bigger numbers) on my screens... Not that it confuses me or anything.
The UK, as is often the case with these things, uses a horrible cursed halfway house system. I have every digital clock I own set to 24h time but know that I would get weird looks if I made plans with someone to meet at 18
Same in Finland for spoken and some written (chat) stuff, that's where most of the time 12h is used, with just "let's meet at six" (no am or pm but clarified if not obvious from context).
Some people use one 24h, other am/pm, but everything related to clocks always has the choice to use one or the other configurable. Most people use 24h format and most public info and tv shows and all that usually uses 24h. When I was a kid am/pm was used in more places, not sure why.
Basically everyone knows how to use both, it's obvious and straightforward, I don't think I've ever seen anyone ever not being able to know the time whichever foat was shown. Am/pm comes more often in informal talking when context of the conversation is obvious since it's much easier to say snack at 3 than snack is at 15.
I never claimed superiority. I only said that since Europeans are accustomed to 24h system, the joke becomes difficult to understand, because we don't have this problem.
But if you perceive this as some sign of superiority, well...
This is where empathy becomes a good skill to have. I'm certain you can understand the basic setup of the joke even though the exact situation may not be likely in your culture.
The joke isn't even about the time, it's about their anxious thinking.