Vegetarian vs animal byproducts?

There is no vegetarian rule book. I'm a lacto-ovo vegetarian, but I don't read all the small print on the ice cream containers, etc. Vegans get into the no animal byproducts thing more then we do. My roommate is a vegan and I'll get after her for putting an animal byproduct (gas) in her car, and driving on a road made from animal byproducts (tar) :-)