Let’s see… An average healthy human male according to any scholarly articles that I’ve found, will create a stream of urine with about 0.35 Newton’s of force, given the pressure of the bladder and diameter of a human Urethra. Obviously Goku isn’t a human, but for the sake of argument we’ll say that a Saiyan must have a relatively similar set of… variables, considering that pure-blooded Saiyans can reproduce with humans.

Mechanically, you pee by relaxing your urethral sphincter and contracting a muscle wall called the detrusor muscle. This is good news for the lethality of Goku’s stream, because his muscles are quite a bit more potent than that of an average human and we can expect significant scaling as a result. Luckily we can use the in-house numbers for an estimate – Goku at SSJ4 is said to have a power level of around 57.6 SEPTILLION. That’s 57.6 times 10 to the 24th power. An athletic human male has a power level at around 10 , so with some quick math:

Goku’s Peeforce = (0.35) x (57 600 000 000 000 000 000 000 000 / 10). I’d also divide this result by an additional ten, which is slightly arbitrary but I figured that Goku, despite his deep love for training his muscles, wouldn’t specifically be training THIS muscle and it’s not like it would scale like a punch.

Goku’s Peeforce ends up being 206 000 000 000 000 000 000 000 N (I think; I suck at math), or 20.6 x 1022. This means that if Goku dropped his pants and let ‘er rip from 1 metre away from an opponent he would transfer an equivalent amount of joules of energy into his “Golden Gallick Gun”, a little less than half of the energy estimated to have been released by the impact of the asteroid that wiped out the dinosaurs.

So as for strongest opponent he could defeat with this unorthodoxed method, I’m not too sure. But let’s hope to Kami that he doesn’t do it on Earth I guess?