This can be a fun fetish! Just a couple of notes. For a woman with no pre existing supply issues the system is set up to respond to demand. Which means, you aren't depriving her baby, you are actually encouraging her body to make More milk! But, breast milk Is a body fluid. There's a reason that as wonderful as breast feeding is for mother and child, said the lactivist, women who are HiV+ are not encouraged to breast feed. I'm too lazy to quote the actual CDC stats, but, some STD's Can cross over, in Both directions and via the fluid itself. a safer sex idea is to offer milk showers instead of straight from the tap!
I know of at least one client this happened to Accidently. His lady friend was riding him cowgirl, came hard, and sprayed all over him!

Orgasm will often trigger letdown.
Kat