RMOAS. When I was in basic training, we hiked to a training area with full packs, including gas masks. The DIs had us all sit (make your buddy smile mode) in a dirt parking lot, while they demonstrated different colored smoke grenades.
They would pop a red grenade taped to a stick, and walk back and forth upwind of the Company saying, "Now this is what red smoke looks like." Then they went to yellow, then green.
When they thought they had lulled everybody into a coma, they popped one with grey smoke. It was CS.
I have never seen 150 people jump instantaneously from a sitting position to 8 ft. high before, but everyone did. When their feet hit the ground again, they ran in all directions like stampeded cattle.
Everybody, that is, but me. When I got a whiff of the CS, I calmly reached down and donned my gas mask, exhaled to clear the mask, and continued to sit there breathing nice, fresh air.
I didn't fit in, either.