I say, "That's gay." It's long past time for me to explain why.
The common wisdom among openminded people is that it's inappropriate to use gay in a perjorative sense, as in "weak, stupid, ineffective." The wisdom stems, I believe, from the impression that this usage of the word links those traits with homosexuality. I don't believe it does. Rather, I am of the view that it's a circular definition which stems from the ridiculous attempt to change the definition of gay to "homosexual" in the first place.
Gay used to mean happy. It was a perfectly nice word. Then some group of wordsmiths managed to get people to start using it instead of "homosexual," which is a long word desperate for a shorter cousin. Gay is a short word, but unless you believe homosexuality can be entirely encompassed by a pale caracature of limp wrists, tittering, and pristine nails, it really doesn't fit. It's two dimensional, shallow, and insulting to try to make that word synonymous with homosexuality, and I don't think it entirely worked.
Granted, gay has entered the English lexicon along with queer and other terms, but I think the language has resisted this change. In fact, it seems to me that the attempt to turn gay into homosexual is "weak, stupid, ineffective." It doesn't make sense. However, the dismal failure of the word has successfully attached itself as a definition.
There is precedent for words receiving meanings unexpected and ironic. Language is guided by the collective will of its speakers, and nothing that does not follow intuitively really ever gets adopted. Hussy comes from the Middle English houswif. A girl was a child of either sex, a knight was a boy, and a counterfeit was once a legitimate copy. We sometimes try very hard to control the meanings of words, but invariably the one that makes the most sense survives in the end.
I never liked gay as a homosexual label, and I think the perjorative definition is more a comment on that usage more than it is on homosexuality itself. I expect the language to give gay up entirely to that perjorative meaning, and finally free the queer community from its insulting associations. I just wish we could move things along and ditch this turd of a word once and for all.