When you accidentally shit yourself and it slides down your leg. Most common when exerting oneself while performing a seemingly easy task. e.g. drinking a glass of water with one hand. Usually used as an exclamative.
"Trump landslide!"
"The bathroom's the third door on your left."
when a male places his scrotum on another persons face (ball in each eye) with the shitter right above the mouth. He then takes a dump causing the shit to roll down their face like a portugese landslide
Woah, has she just recieved a portugese landslide?
I gave him a portugese landslide the other day.
When you jizz in your girl's hair before throwing her down a flight of stairs, with a pre-organised acquaintance waving a red cape at the bottom of said flight of stairs, calling appropriate Matadorial phrases.
Guy 1: Dude I'd just had the best fajita ive ever eaten, so I celebrated by giving my bird a spanish landslide.