Besides comical effect?
He and the rest of the Rat Patrol Team are either running covert operations or involved in one gun fight or the other. Under those sort of conditions, he probably holds it in too long to avoid discovery or to get through a battle.
Though it is most likely due to Kojima's sense of humor.
Note this is merely speculation. There is no in-game explanation of this phenomenon.
you go to the fossil maniac's house and the kid in front of the tunnel gives it to you. but only if you have the TM poop your pants
no
you dont
it makes you have unlimited ammo
its available when you get the mkII
people poop their pants from the ages 0 to 4
because she saw you poo you pants
no
no
Laugh, because you have my poop in your pants.
Laxatives!
No
yesss m'm
Everybody poops. Babies who have not been trained to use a toilet will naturally poop their pants, for lack of a better place to put it.
Every day
Rosie O'Donald
Yes. often actually.