Well, it didn't take as long as you would expect. Let me tell you how it happened.
One of the first men to roam the Earth searched for days for water, but was unsuccessful. On the supposed last day of his short life, he wanted to somehow get some taste into his mouth. Somehow, he found himself coughing. Then his wife came over and gave him some water.
He continued to cough, and eventually that coughing turned into laughing.