Nothing humorous about breaking your humerus ... just ask Lindsey Vonn who cracked her upper arm bone during a bad crash at Thursday's ski practice.
Vonn was hitting the slopes in Copper, Colorado when she lost control and bailed hard -- breaking her arm bone badly.
Vonn says she was rushed to Vail, CO immediately and underwent surgery that same night -- where doctors used a plate and screws to put the bone back together.
"I will work my hardest to be back on the slopes as soon as I can, as I always do," Vonn added.
"Thanks for all of your continued support."