How is the act of repeatedly leaving and entering swim form regarded in the inkfish world? I’ve heard from a few people that it’s considered pretty rude to some.
Depends on the culture and the situation, really.
A few cultures regard swim form entirely as taboo or risque, as you appear "naked". Some think it's rude when you're talking to someone, as you have much more limited facial expressions. Most think it's fine, just situational.
The rapid shifting in and out is (in cultures where swim form is fine in public), oftentimes very situational. It's usually regarded as an act of extreme emotion- like how some people just need to wiggle or move when they get really happy, or excited, or even frustrated.
In the times where it's clearly friendly/excited, because of the mimic nature of squids, others often join in. This is usually called a party, or squid party, and is fine!
Doing so after you've killed someone or defeated them, however, is often regarded as a taunt, and extremely rude- a way to say "haha I'm happy cus I beat you!!!"
So... just like lots of gestures, really situational.