WETSU stands for "We Eat This Shit Up". Most commonly seen on Valley View Cougars 6th Man t-shirts. Why because WE EAT THIS SHIT UP in the bleachers.
Picture this your team is up in the 4th quarter and you have your 6th man t-shirt on and the other team is losing because of the 6th man, you start to chant "WETSU" and pointing to the back of your shirt towards the other school's student section. It demoralizes them.