The reason not to blow/suck pitot/static tubes/ports is only in part the risk that a healthy lung could over pressure. More concerning is the rate at which a person can apply the pressure change, perhaps damaging an altimeter or airspeed mechanism, whose gears and sectors cannot move that quickly without stripping something. No GA ASI was ever designed to go from zero to 200 in one second - there's still inertia in the mechanism, appropriate to normal flying. Similarly, on the test bench, I'm very cautious as to the rate of pressure change, my test bench will change pressure much more quickly that the instrument can withstand. On occasion, one may see an ASI with the pointer lying in the bottom of the glass - too rapid a pressure change spun the pointer off ... $$$.
Last good reason, if someone has had pitot heat on, blowing into it is likely to be injurious.
So, as warnings clearly state, do not blow into pitot static tubes/ports.
Edit to add: I just experimented on my mercury manometer, and I could mouth blow a pressure of 1.5 PSI, which equates to about 275 MPH. My 58 year old lungs are not a testament to health, thougth apparently adequate! This value exceeded the limits of my merium fluid manometer, so I could not get a more precise speed value. In any case, my blowing into a GA airplane pitot tube has the potential to cause damage - so I won't do it.