I vaguely remember someone doing this during a conversation in a bar in Japan years ago, and I saw it again in a manga. What does this mean, if anything? I don’t remember what the conversation was about, and we were all drinking so I wouldn’t trust my memory anyway
If you’re western this is old-timey for “I’m about to dive into a swimming pool, or the ocean.”
lol I 100% did this as a six year old to dive into a pool during swim lessons
we used the moniker “zip” “T” “zoom” to do the back stroke