That is a great deconstruction! *thinks* It's clarifying for me when and why "lame" is derogatory... a lame excuse is a feeble excuse, a lame leg is a lame leg, (and it's a common term for horses), and those are accurate terms. But when someone says, "Oh, you're so lame for not coming out with us tonight and doing X instead," which has become very casual and accepted speech, it seems like the underlying subtext is-- "you are weak and feeble, therefore unacceptable/uncool". It creeps in.