This is a fascinating one because that word is shifting again: "gay" increasingly means "lame" rather than "homosexual". What's fascinating is how this is happening even as society becomes more tolerant of homosexuality. Young people who use "gay" this way belong to probably the least homophobic generation ever, so the politically correct misreading of this shift is even more off-base than political correctness usually is.
The South Park guys captured this perfectly with their line, "This is gayer than sex with men!"
All this by way of agreeing with you that the subtleties of language far surpass people's rigid attempts to nail them down. Incorrect usages that gain currency turn into correct usages. It's more interesting to observe and admire these shifts than to try to stop them (a fool's errand).
Edit: Man acts as though he were the shaper and master of language, while in fact language remains the master of man. - Heidegger