Probably “sluta vara en så lagom rolig person”. It isn’t directly an insult. However, it’s not something you would love to hear. It translates to “stop being a person who has the just right amount of fun”.
Another thing my friends say when they are med is: “Din jävla ångvält!” which translates to “You fucking steamroller!”.
It just sounds much better in Swedish.
A fire extinguisher can be found for less than 100 USD and is a must-have. A smoke detector is also a bare minimum in my opinion.
https://imgur.com/a/WaNtPRI