n other people's privates, if a player hits you (while you are wearing this helmet), kamikaze bees will fly out, capable of causing damage to players in their private when the PvP flag is turned off.

Metas:
Item.of('productivebees:bee_nest_diamond_helmet', '{Damage:0}') - Bee's Nest Helmet

https://www.youtube.com/watch?v=WlkKHvuyfl4

why is the other player able to hit you if PvP is turned off?

Players not added to the region may be beaten. PvP is disabled. You cannot defeat players added to the region.

which mod is responsible for that?

I can't do anything about a plugin, it lives outside the mod world.

plugin world guard

Ok. Thank you