You don't need keys or an engine to kill people in a car.
Neither is car needed to kill someone... What's the logic behind that?
Drinking in public places is in Poland illegal, so, paradoxally, drinking in a parked car seems to be "less illegal" than doing it outside.
The regulation (the Act on Upbringing in Sobriety) states:
Art. 14. 1. It is forbidden to sell, serve and consume alcoholic drinks:
1) in the areas of schools, other places of upbringing and education, and student dormitories;
2) in the areas of working places and places of collective feeding of employees (meaning canteens and cafeterias in working places);
3) in the places and time of mass people meetings;
4) in the means of public transportation, except for restaurant carriages and cafeterias on trains, where it is allowed to sell, serve and consume alcoholic drinks containing up to 4,5% of alcohol and beer;
6) in the places occupied by military and internal affairs institutions, as well as in the areas of barracks and temporary acommodation of military units.[/b]
2a. It is forbidden to consume alcoholic drinks in streets, squares and parks, except for the places dedicated for consuming them on the spot, in the places of selling these drinks.[/b]
3. It is forbidden to sell, serve and consume drinks containing more than 18% of alcohol in training sites.
4. It is forbidden to sell, serve and consume drinks containing more than 18% of alcohol in places of holiday accomodation.
5. Selling, serving and consuming alcoholic drinks containing more than 4,5% of alcohol on open-air events can take place only with a special permission and only in specially dedicated places.
6. In other, not mentioned, places and areas of a municipality, taking into account their character, the municipality council can introduce a temporary or a permanent ban on sale, serving, consuming and bringing alcoholic drinks.
7. The minister proper for the affairs of transportation and the minister proper for the affairs of sea economy, by means of a regulation (executive act), shall define the rules and conditions of selling, serving and consuming alcoholic drinks on the sea trade ships in international transportation, on the trains and aeroplanes in international transportation, and within international sea ports and airports.
8. The minister proper for the foreign affairs shall, by means of a regulation, the cases and opportunities, in which, taking into account the international customs, it is allowed to serve and consume small amounts of alcoholic drinks.
If the car is parked on the street... it's difficult to say whether drinking in it is legal, or not. But the same holds for both the person sitting behind the wheel and at a passenger seat.
Of course, when a policeman sees that, he will rather not want to discuss with you; he will want to give you a fine ticket, and you can either accept it, or not. If not, then they will take you to court, which will evaluate the situation, whether it was legal, or not (if not, then you pay both the fine and the court costs)...
There is an article on that here:
Police cannot confiscate your driving license for drinking in a parked car (so it doesn't violate the regulation on drinking and driving). But in the case described in the article it was so, and the court decided that the police was right, because the guy who drank in a car didn't have any evidence on that he didn't drive that car... And there was a witness claiming that he drank before he came to that parking lot.