we generally try to ignore bad manners of tourists. I can suggest to don't chew noisily while eating, galateo for us is pretty important to keep, plus try to don't imitate hand gesture too much, it's not always funny haha
if someone offers you food or coffee it's always recommended to accept it, most of us are generous and try to make you comfortable.
Also, when tourists visit churches not always follow the rules, they are reported at the entrance. I think it's all :)