I think it's always better to stand up for yourself in an argument, even if it means really pissing the other person off. Maybe they'll stay mad at you forever, but they will probably cool off and have a begrudging respect for you. Sometimes this kind of argument can actually improve a friendship. The other possibility is for you to back down and agree all the time, which will make things more comfortable in the short run, but will result in the other person losing respect for you.

I think having someone mad at you, even if it is forever, is better than having them lose respect for you. I can deal with someone being angry with me and doing stuff to try and piss me off. But once someone loses respect for you, there really isn't any going back.