Cairo may seem large and confusing, but it is easy enough to pick up the basics. Here are a few random things that I have learned.
Crossing the road in Cairo is straightforward for anyone who is reasonably expert at the videogame "Frogger". One noteworthy difference is that in "Frogger", when your pixelated frog is crushed by a fast-moving truck, you still have another two lives.
Every single street corner in Cairo has its own grubby, battered stray cat.
Egyptians are friendly people, but it is not uncommon for fights - or, strictly shouting and shoving matches - to break out. As in many other countries, the probability of a fight starting is directly proportional to your proximity to a taxi stand. When a fight does break out, a small crowd will quickly gather, with some people there just to watch and others spontaneously siding with one or other participants. If the original disputants need to leave for any reason - to go get a coffee, or go to the office, for example - the newcomers will keep the argument going until they return.
There are probably more romantic places to make out than a dirty stairwell filled with broken office furniture and cat shit, but they are apparently not accessible to Cairo teenagers.
Egyptians have been taught to respond to the sight of a foreigner by smiling broadly and saying
"Welcome to Egypt" in English. A tiny minority apparently have trouble mastering the correct sounds, so that their greeting comes out sounding more like
"Fuck you" or
"Get out America".
Shopping districts in Cairo are highly specialized. For example, one area might contain only shops selling car parts, while another will be completely given over to shoes or lamps. This has two implications. One is that if you happen to start feeling hungry or thirsty anywhere in the auto spares district, you're out of luck: you can walk for days without seeing anything except hubcaps and mufflers. The other is that somewhere there must be an entire neighborhood filled with small convenience stores selling bottled water and snacks. If there is, I never found it.
Flyovers and minarets should not be used as landmarks, because they are everywhere in the city and they all look alike.
To judge by the smell, every cat in history has pissed in the burial chamber in the Red Pyramid at Dahshur.