You are here because Tamatoa from the Disney movie Moana sang to look up the word decapod, and you searched it up for fun to see if anyone referenced the movie on Urban Dictionary. You are right.
"...You could try, try, try but you can't expect a demi-god to beat a decapod, look it up..." - Tamatoa, 'Shiny'.
An act of masturbation in which, while one pleasures themself, they decapitate themself with a rusty shovel or dime store katana at the verge of climax. Then, whilst their head rolls away, they attempt to catch the load in their mouth within the final three seconds of life.