Dare you to cough

The owner of a drug store walks in to find a guy leaning heavily against a wall. The owner asks the clerk, "What's with that guy over there by the wall?"

The clerk says, "Well, he came in here this morning to get something for his cough. I couldn't find the cough syrup, so I gave him an entire bottle of laxative."

The owner says, "You idiot! You can't treat a cough with laxatives!"

The clerk says, "Oh yeah? Look at him, he's afraid to cough!"