I've actually been surprised at how little sea water hurts. It's my very strong instinct to close my eyes when my mask is removed, and it's not a good thing for me to do, because I get disoriented that way. Opening my eyes actually gives me a TON of useful information to remain oriented and stable, and even in ice cold water, really isn't that uncomfortable. I've never had any conjunctival irritation afterward, although even a small amount of pool water will render me uncomfortable for a full day.
I completely agree with TSM.
My first reaction would be to look around briefly for my mask, and to note any large blobs in my vicinity that may have caused my mask to come off.
My next reaction would be to reach into my right cargo pocket on my drysuit or wetsuit and retrieve my spare mask.
My third reaction would be to grab my knife or spear and deal with the large blob that caused my mask to come off.
Everyone who dives with me knows not to touch my gear, tanks, or mask. My twin 130 tanks and perfect hogarthian configuration convey that message in strength.
It is important always to maintain and adjust for neutral buoyancy, with regular breathing, in order to stay neutral at your depth while you do are doing all this. Because the worst that can happen is that you begin to drift downward, where a whole host of things can go wrong, or else to drift upwards, and end up with an uncontrolled ascent, where another host of things can go wrong.
I do not believe it is smart to go around ripping off other people's masks, and therefore I do not enroll in courses where the threat of this happening is possible.
I have been in a situation where my mask failed due to being stepped on before the dive. Now I keep my 2 masks inside of the foot pockets of my fins, anytime they are not either on my face or in my cargo pocket, to protect them.