"Wot's in da canistah" he says and then adds "i could tell ya but then i have to kill ya"
Forget that selfish prick. I will tell you whats in the canister. And i wont even have to kill you. Plus you'll learn how to counter Smoke easily.

You are in a battle against 5 well trained operators. They don't know about fear, doubt or failure. They only want to kill you, either using guns or gadget. Remember my dude ! How many times you have died because of Kapkan traps, Lesion mines, Frost's mats or C4 explosives ? I don't need to tell you how deadly or painfull these are.
In that fierce battle you see some dude with smoke mask and throwing yellow gas to you. Don't you think "oh look at these guys, they are and their gadgets must be deadly. I must run away from that yellow gas" ?

Yeah! You saw a yellow gas and thought "this must be deadly". Right, do you know anything about "Placebo effect" ? It's something like that: doctor says "take this pill and you'll be ok" and then you took the pill and you get better. But the pill is a fake medicine, it's just a candy. Candies can't heal your sickness. The gas! the gas is just "Placebo" it's a fake gas.
Yes, my children, i can hear you saying "But it hurts, why does it hurt if it's a fake gas?" because you think it's a harmful gas my child. It's only on your mind. Pain is only on your mind. Did you ever see someone died because of Smoke's gas ? Well my answer is no. Because killing with a fake gas is not possible. And for God's sake think about it a moment. What would you do if you get a perfect formula. Would you tell it's ingridients to scare people more or would you be like "uuh don't ask the formula dude, becasue i have to kill you if i tell you" the second one sounds like a man who has no secret formula but who is trying to scare people, doesn't it ?

Now you know Smoke's gas is fake. You know it can't hurt you or kill you. Here is how to counter that liar maggot.
There are 2 ways to counter smoke gas
Asserting dominance: Next time when yo see smoke gas run through in it, it will not hurt you, it can't, because you know its just a yellow gas. Smoke will probably think "no one can pass my gas" and he will not look behind. But you'll pass through the gas and stap that schimigity Smoke from the back.
Using enemie's power to against him: This is a more complicated strat but it's better in my opinion. When you see smoke's gas run through it and start crying inside the gas. You start mourning like "Oh my, God why this gas is so painfull, it hurts every part of my body, oh god i can't stand that pain, no one can heal me now, even the god can't help me". At this point Smoke will think " my gas must be really dangerous, oh god i only thought it's just a harmless yellow gas, i breathed the gas before ! i don't want to die, i want to live" but it was over for him my friends. And he will die because he thinks his gas is really harmfull.

I am not good at conclusions. Instead of here is a life tip for you from me
Whenever you leave an empty room alwasy say "I know you are here, you can no longer hide, it doesn't matter that you hear all the things i spoke". If the room is really empty there will be no problem but if there is someone in that room who's listening, you'll become so cool in his eyes, he will think you are some kind of secret agent.