How do i mute myself?

I try muting myself but it never seems to actually mute me. I find it very hard to be tactical when i'm worried that my team can hear me shotgun in hand breathing into the mic like a dying gazelle in the middle of the chihuahuan desert.

Then again i can imagine nothing scarier than my half conscious body knife in one hand grenade in the other running at someone 27.8mph, breathing hard enough to make people think that a hurricane harvey's back with a vengeance.