Which results in them all laughing and the mother accuses her son for always playing tricks with his friends teaching them to say bad things.
By bad things, do you mean swearing or being vulgar? If not, then when I first started learning Polish I kept confusing Włochy and włosy and also śmieci and śmierć - I did actually ask whether death was included in the czynsz on a flat. I also asked for those biccies, Delicje pomidorowe instead of pomarańczowe. You should have seen the face on the girl in the shop.
'Ale nie ma'.
'Ale jest' I insisted. 'tam na półce'.
'JEST??? she responded in justifiable amazement turning to look at the shelf. Then the penny dropped 'ah pomarańćowe
'. She didn't even smile, let alone laugh. I did though :D