How do people know HCN smells like almonds? I was told by my chemistry teacher that $\ce{HCN}$ smells like almonds. She then went on to tell a story about how some of her students tried to play a prank on her by pouring almond extract down the drain to make her think that they had inadvertently created $\ce{HCN}$ gas. She said that she knew that it wasn't $\ce{HCN}$ because if she had smelled the almond scent, then she would have already been dead.

I never asked her, but how do people know $\ce{HCN}$ smells like almonds if they would die before they knew what it smells like?
The odour threshold for hydrogen cyanide $(\ce{HCN})$ is in fact quite a bit lower than the lethal toxicity threshold. Data for $\ce{HCN}$ can be found in many places, but here and here are a couple of good references. That subset of the human population that can detect bitter almonds do so at a threshold of $0.58$ to $\pu{5 ppm}$. The lethal exposure dose is upwards of $\pu{135 ppm}$. That's a whole $\pu{100 ppm}$ range in which to detect and report the fragrant properties.