The use of offensive words as slang.

[Mystyrion]

I really didn't know how to coin this topic so, I apologize.
And I realize this may be a touchy subject for some, I don't intend to offend anyone, I just want opinions. So again if you find anything I say offensive, I'm sorry.

The title stems from using the offensive words to a particular race, gender, sexual preference, religion, etc.
Words like Gay, Fag, Jew'd, The N word, Ginger, etc.

Now my question is, is it okay to use these words in a non contextual way that doesn't reference the actual meaning of the word or in other words using the slang meaning.

For Example: On July 5th a friend posted on Facebook that he disliked Fireworks and they kept him up late, which resulted in a lack of sleep for work the next day.
I simply posted that Fireworks are gay and my explanation on why they were gay. Gay of course meaning lame or stupid.
Two female posters then immediately posted after I used the word Gay immediately attacking me, saying that I had no respect for the gay community and I was being very disrespectful. Something along the line of me treating them like a second class citizen.

I realize that they may have overreacted to the subject at hand. Obviously coming out and bashing someone who meant no harm isn't the best way to get me to apologize for what I just said.
I responded with something along the lines of "I'm sorry to have offended you, but the context in which I used the word was in no way referencing the gay community at all and that I was using the slang meaning of the word which meant lame or stupid."
They responded that if its not in the dictionary then its not a real definition. I pointed out that the slang definition of the word was actually in the largest online dictionary of the English language. The conversation stemmed into one of them posting about how they get treated like a second class citizen, I pointed out that their opinions aren't valued any lower or higher than mine and reminded them that I meant it in no harm and left the conversation at that.

I'm not necessarily saying that I'm right in the conversation I stated above with those women, I just wanted your opinion.