It really isn't a French thing to be mortified by people speaking English. Probably, you did something else to offend. That said it doesn't hurt for bonjour to

It really isn't a French thing to be mortified by people speaking English. Probably, you did something else to offend. That said it doesn't hurt for bonjour to be the first word out of your mouth. It is France and they speak French after all. The same goes for hello in every other language in every other country on earth as well. source: American who has lived in France.