Can you clarify the difference you see, if any, between what you understand "ethics" to refer to when used by an average person, and what you understand "peer pressure" to refer to?
Peer pressure is moral in nature if people think of it that way. I can't provide an ontologically basic definition of social morality, but given that you are a human, I'm pretty sure you can identify it when you see it. Pressures within a group that serve to help the group function better are usually moral in nature.
It seems to me that usually, when someone says "ethics" on lesswrong, ey usually means something along the lines of decision theory. When an average person says "ethics", ey is usually referring to a system of intuitions and social pressures designed to influence the behavior of members of a group. I think that a lot of the disagreement regarding ethics (i.e. consequentialism vs deontology) is rooted in a failure to properly distinguish between decision theory and what society pressures people to do. Most lesswrong users probably understand the distinction fairly clearly, but we only ever talk about decision theory. Why don't we talk about the social meaning of ethics?