I did not find the story unrealistic as other users have commented. Actually I know quite a few guys and girls -of different nationalities- that live or have lived with their parents not because they could not afford to live on their own but also because it is... convenient.<br /><br />It is not difficult to understand why someone would still prefer to live with his parents under these circumstances - he lives as he would in an expensive and comfortable hotel (minus the bill!). Everything is taken care of by somebody else (cleaning up after him in the bathroom, laundry & ironing, bills, shopping, preparing dinner etc), he does not have to buy a car since he can use his parents' cars, he does not have to spend his money on everyday's life necessities and he can concentrate without a single worry in his mind on whatever pleases him (e.g. being an eternal student and having a different girl every night in his bed). In a few words : he's just spoiled. You can see when he tries to live on his own that he does not even make an effort, and immediately pre-judges that he could not possibly make it on his own. He does not want to live on his own and lose all the comforts he currently enjoys.<br /><br />Plausibility of the story apart, I've seen the movie three times and each time I found it equally laugh-out-loud funny - a very successful combination of well-written dialogues and very good performances by the three lead actors (especially Sabine Azema and Andre Dussolier who are playing the two parents).