There is no polite way to navigate telling your coworker that they have bad breath.
Obviously, this is a delicate situation, and you might as well do nothing if you're a conflict avoidant personality. At the end of the day, it really depends on how poor the hygiene is. After all, you never know how this person might react to being called out even in the most sensitively handled manner. You also don't know if the reason behind said bad breath goes beyond poor hygiene. Then, the person who is out of line is not the person who can't keep his breath clean; it's the person who pointed out someone else's condition in a work environment.
This employee had the unfortunate experience of being paired out with his smelly coworker on a collaborative project that required them to share a desk and a laptop with limited personal space... for six hours straight. Imagine being less than six feet away from your least hygienic coworker for practically the entire work day.
Keep scrolling below to find out how the employee endured it and what happened when he tried to send a signal...