I accidentally switched my pi 3 off and on again a few times directly after each (few secs) other by pulling the plug a few times. :/ Can my pi be damaged by this? Everything seems to be working still.
Not very likely just by pulling the plug, no, even if you do it multiple times in a row.
Pulling the plug suddenly does run a slight risk of corrupting data on the SD card, but although this may create a hassle for you this is not permanent physical damage. It is also generally unlikely unless the pi is very busy at the time. Doing it rapidly in succession will probably not increase the risk although this depends on the propensity of the pi to cause corruption by spiking voltage to the reader, which I cannot say for sure it does not (but I do not think so).
When powering through the microUSB jack, there is a polyfuse which will protect the pi from current surges, so the worst thing that may happen is this polyfuse is triggered and you have to wait some hours or perhaps even days for things to work again. This is pretty unlikely as well, although it may depend on what else is attached to the pi (I think it would take a lot, so much so you would be aware of the risk).
Of course, there is no accounting for defective power supplies or pis themselves, but the same is true of the brakes in your car, etc.