The first time I ever got head, I blew a big, sudden load into the back of my then-gf's throat. She kinda just reacted by swallowing it, and didn't seem to mind too much, although she said it was her first time. I think she didnt mind because I blew it past her taste buds into the back of her throat.
Nowadays, when I get head, I dont give a girl the courtesy warning of "Im gonna cum!". I just hold it as long as I can, and let it rip when I cant hold on any longer. Its not my fault if she is too stupid to read my obvious body language. If she swallows, I make sure to give her positive reinforcement for the desired behavior.