Hank Green from the YouTube channel SciShow explains here why smoke always insists on blowing straight in the face of someone when grilling sausages in the fireplace in the garden. According to the laws of physics, it is because you block the air flow, which means that the smoke can move where you stand.
…the real key to understanding why smoke keeps blowing in your face is that the rising air doesn’t just rise on its own. It is pushed by the air around it. Because when hot air moves away from the fire, the air that pushed it keeps right on going and fills the gap that the hot air left behind. And this is where you come in.