Why human cannot inhale carbon dioxide?

Humans cannot inhale carbon dioxide because carbon dioxide is present in a very small concentration in the air.

If humans inhale more carbon dioxide from the room with a high concentration of carbon dioxide, a high concentration of CO₂ displace oxygen in the air.

It can cause difficulty in breathing with symptoms like rapid breathing, rapid heart rate, clumsiness, fatigue, etc. It can also cause nausea and vomiting, collapse, and even death.