Going at it in the car, OK. Leaving the car running, in the garage, with the door closed... not so good:

A Milwaukee man and a 17-year-old girl died of carbon monoxide poisoning while having sex inside a running car in a closed garage last week, according to a Milwaukee County medical examiner's investigation report.

But wait! There's more!

The man's mother said the dead 17-year-old was not her son's girlfriend, and she did not know her, according to the report.

I remember something like this happening in my area when I was in High School, so it's probably more common than people think. Somewhere Darwin has his fist in the air with this two-for-one.