pen / Ben — P is not B

Fakh lel Lebnéniyye! L /p/ ma fi bil 3arabe, so your mouth defaults to B and every 'pen' becomes a 'Ben', every 'cheap' a 'cheeb'. Sakkir shaftak w fajjir shwayyet hawa — pop the lips with a puff of air. Without that puff, P and B sound identical.