A couple assume the 69 position with the woman on top.
Just before ejaculation, the man brings his legs up and locks the woman's head down on the penis.
At the exact moment of ejaculation the man farts, causing a faceful of fart and semen for said woman
The Viking Longboat is best performed after Mexican or Indian food for the perfect finish
Dude 1: ''I was 69ing with Angie last night and I decided to Viking Longboat her!''
Dude 2: ''DUDE! Did the fart stink?''
Dude 1: ''Hell yeah it did! I ate like twelve burritos the night before!''
Dude 2: ''DUDE!''