Question

What happens when two plates made of oceanic crust collide

Answer 1

Oceanic  crust is denser / thinner than continental crust so the denser oceanic  crust is going to bend and get pulled under the thicker/stronger continental crust.

Answer 2

When two plates of oceanic crust collide it can result in earthquakes and can potentially cause a tsunami if powerful enough. The crust can separate and subduction can occur.