We just returned from a trip to Egypt and I figured out a fairly effective way of dealing with hassles :-)
At the beginng of our trip. I was doing what most people on this forum recommended: a firm "La Shukran". Guess what, that never stopped the hassling. The street vendors literally hassle you to death :-)
At luxor, we asked for directions to the local souk from this British woman who is now living there, while a guy hassled us from the side. I gave the British lady full credit because she turned around and stood in front of the guy with her face literally three inches :-) away from his and said "La Shukran". The guy retreated. Since I couldn't muster the courage to position my face that close to a local's :-), this is the strategy I developed over the days: pretend you don't understand them.
It may sound dumb, but it worked fairly well. Dont' bother with the "La Shukran" because the hasslers never stop at that. Just completely ignore them and keep walking. Let them do all the talking because there is nothing in the world that could stop them other than some kind of open confrontation.
I chucked internally as I noticed the street vendor's reaction to my complete ignoring of them. As we are ethnically Asian, they tried to accost us first in Japanese, followed by Chinese, then Korean, then English. :-) It first startled me, and then greatly amused me when we walked past this store in which two men were literally bowing to us at 90 degree angle. They must have thought us Japanese! If they meant to get attention, they surely got ours :-)
It may sound rude to ignore the hasslers, but really what could you possibly do ? I found a "La Shukran" was always followed by more persuasions, or questions like "where are you from ", "what is your name"... It is the same with every street vendor and if you want to be polite after a long day's tour and all that heat, prepare for a sore throat and lost voice.
The only place I kind of lost my cool was Khan el Khalili. There the people not only hassle you, they sometimes get a little physical. For more than one time, a vendor would approach me and upon my ignoring him, placed his hand on my arm and tried to "guide" me to his store. It was at these moments that I would turn around and look the man in the eyes and tell him word by word "Don't touch me!". And it worked every time.
We loved all the sights we saw in Egypt, but I really doubt if we would ever return to that country. It's anything but relaxing.