Should I sprinkle a mouse with calcium before giving it to my corn snake? I was sure they need calcium but a very experienced snake owner said no need to do that.
The reason I'm asking is that I'm afraid he'll develop rickets.

that snake owner was right no need to do that. i've never seen snakes with rickets if they are fed mice. as a general rule if a snake needs vitamins they are given as an injection.
if your snake seems a little malnourished i would do it with a multivitamin designed for snakes .. . i would consult a vet before hand tho and mesleeve3 is correct there ... they are usually given as a shot, they really dont need calcium as they get quite a bit from the food they eat