The English language is a complex tapestry of varying rules of grammar, spelling and uses. Individual words can hold multitudes of meanings and evolve over generations. Sometimes those meanings can evolve into ones that are hurtful and silencing. We have control over this and we can keep words from being hurtful by not using them in damaging contexts.
Words mean things.
I can't believe we're still having this conversation but here goes:
When you say something is gay when you really mean stupid, you are equating gay with stupid. It paints gayness as a negative trait, and it's not. Full stop. When you use this, you are insulting and marginalizing an entire group of people. Same with retarded. Hell, even same with lame.
Using the word stupid all the time gets boring, I know. And these can be difficult linguistic habits to break (believe me.. I've stuck my foot in my mouth on more than one occasion... Right Danno?
So for your convenience, here is a handy list of words that can be used in place of stupid that DON'T serve to marginalized entire groups of people for no good reason.
Lacking common sense
fucked up beyond comprehension
Of course, some of these are better suited to some contexts more than others. This isn't even a comprehensive list. Your Thesaurus has all these and more. I hear they even have em online now.
Yeah. You're welcome.
My readers are helpful. See also:
Feel free to add suggestions in the comments.