Metal Gear Solid 4: Guns of the Patriots Easter eggs

When tracking Naomi in Act 2, look to the right when crossing the river to see a guard relieving himself.

Follow the resistance member in Act 3 to see him urinating in the fountain in the small park.

In the central park during Act 3, there is a statue that Snake can interact and imitate. Stay in that pose until a resistance member appears, and he will urinate on you.