The man says, "Sorry, officer, I can't do that. I am an asthmatic. If I do that, I'll have a really bad asthma attack."
"Okay, fine. I need you to come down to the station to give a blood sample."
"I can't do that either. I am a haemophiliac. If I do that,I'll bleed to death."
"Well, then, we need a urine sample."
"I'm sorry, officer, I can't do that either. I am also a diabetic. If I do that, I'll get really low blood sugar."
"All right, then I need you to come out here and walk this white line."
"I can't do that, officer."
"Because I'm drunk."