From that logic, should I put the response in the subject line as well? I don't know if it's rude or not, but seriously, if the entire email fits in the subjec

From that logic, should I put the response in the subject line as well? I don't know if it's rude or not, but seriously, if the entire email fits in the subject line, don't send an email. Send an IM, Slack message, Tweet, whatever, why use email at that point.