If an ally's heavy melee hits the same moment viscous uncubes, they can be parried just like enemies.
This is probably the same incident that allowed allies to kill eachother if attacking during the same frame cube is removed.
I tried finding what this green icon on profile means, however I didn't find anything bound to backslash in settings, and using "unbind \" in console also does nothing.
It's not push to talk, unless it's somehow bound to that key somewhere else.
Pressing that key whenever there's any other...