Also, lets not forget that the initial suggestion is still a hoax, as there is no way that a barrel connector can do anything when stuck into a 3.5mm jack, as there isn't any way to make contact with the inside of the barrel. Which is lucky as he is proposing putting 5V in, and if you succeed somehow to put 5V on the 3V3 supply its will blow eventually The video is just a lie!
Also, yes its very possible to damage your PI, even when you succeed in putting exactly 3V3 on the 3V3 line (and you would need to put a diode drop (0,5V) more in to do that! When you do, and you do not connect a 5V supply then the NCP1117-3V3 voltage regulator (RG2) has no input voltage, and a 3,3V forced output voltage, which isn't a good scenario for a low drop regulator, you will damage it eventually. In fact in some schematics where this could happen you always see a diode between the output an input of the regulator so that if the input voltage is somehow lower than the input voltage the diode makes sure that the input is at least at (almost) the same voltage as its output. See figure 25 of the datasheet of the device, which can be found here:
for an example of this diode used.
Lastly its possible that when you do this you are trying to put in excess of 500mA through a very small (double) diode, the BAV99, which is normally rated at just 100mA or so!
If you are desperate for an alternative way to power the PI, (when transporting it, yeah, right...
) then I suggest putting in 5V via the GPIO pins!