Humorous ideas for a get well card message include joking that the recipient is faking his illness for time off or congratulating him on the special treatment he's going to receive. A humorous get well card can improve the recipient's mood and make his recovery easier.
One way to accuse the recipient of faking his illness is by writing "Who do you think you are to take time off from your job?" The writer can also tell the recipient not to worry because his work isn't going anywhere, and that it's going to be stacked high when he returns.
To mention the recipient's special treatment, the writer could say "Congratulations on being sick; enjoy your royal treatment." He can also mention the recipient's opportunity to get his beauty sleep.
If the recipient has a serious disease, the writer can say that he feels sorry for the disease, because it doesn't stand a chance.
A humorous message in a get well card isn't always appropriate. These types of messages are usually received best when the recipient enjoys jokes and isn't too serious. Humorous messages can make the writer appear uncaring or offend the recipient, especially if he has a serious condition. As a general rule, if the writer thinks the recipient could take any offense to his joke, he shouldn't write it.