Brain freeze has appeared in two episodes.
Brain Freeze in "The Thrice Cream Man"
Like in real life, Mung and Schnitzel get brain freeze when they eat thrice cream too fast. Their heads became surrounded by blocks of ice.
Brain Freeze in "The Brain Freeze"
In "The Brain Freeze," brain freeze is shown as more of a parasyte. It even tries creating things to prevent the victim from escaping the brain freeze.