There was a Norwegian submarine on lookout for enemy ships south of Norway. The Swedes thought it would be fun to mess with them. So a Swedish diver swims to the submarine and knocks on the hatch. Naturally the Norwegian opens the hatch and boom the submarine sinks.
The Norwegian submarine crew gets another submarine as replacement and does the same mission. So of course the Swede swims down to the sub and knocks on the hatch. To the Swedes suprise the same Norwegian opens the hatch so that the submarine sinks once again.
The Norwegian crew gets one more submarine so that they can keep going with the mission. The Swede couldn’t retain himself so he went down to the sub and knocks on the hatch one more time. The Norwegian opens the hatch and says: -Haha I’m not falling for that again!