I'm not absolutely sure, but I think that the convention of not using the left hand is more of an Islamic thing than AE.
There are many representations of people using left hands in Egyptian art. The one that comes immediately to mind is on Namer's palette. The man standing behind the king has the king's sandals in his left hand.
The use of the left in modern Egypt is seen as a mark of dis-respect. The left is used while going to the bathroom. Using the left to eat, to touch people, etc. is viewed poorly.
I'm left-handed. Imagine, if you will, the looks I got when eating at cafes in Cairo!