Get unscented cans to reduce or eliminate the sting. I've found Gillette red cans work the absolute best and are worth paying slightly more for. You can also let the foam sit for as few minutes in the pie tin of you want but I haven't found this to be necessary.
As people have probably already said, letting it sit for a while when exposed to air should bring down the chance of it stinging or reduce the sting by a bit. However, letting it sit unattended for too long will cause the foam to become soapy, but it's highly unlikely to happen if you just mix it up a bit. I hear that when you use shaving foam to make slime the sting is greatly reduced when you mix with a little water to make it a bit thinner so it will pour, but I have no experience with it personally.
i will tell you, if you have hair color at all and play in it it will STRIP your color by so many shades! it is hard for me because my natural color is brown but i color it dark brown and it strips it to a reddish color. also, we have noticed our bodies start to feel cold if we have been in it a while, then tingly where it is really nice but if you get it in your eyes after a while it will burn. if you get it in your "parts" after about 20 minutes, it can burn. if you have sensitive skin, i would either mix it with something else, or get the name brand for sensitive skin because it will give you a sort of burning, itching skin once you get out of the shower. one of my favorite substances but can come with some side effects! i love mixing it with different stuff to make really neato substances! it is deffo one of my favorites. we found that shaving foam and methycellulose is an amazing mix! we just cant find any mehyl that mixes right anymore!! crazy!