To call it "offensive" may be a bit strong (though I'd say it's offensive to those of us who enjoy good use of language ;) ), but exclusive? Sure. It links superior programming and masculinity.
You're sitting in a conference room full of women who are developers, and you start saying, "So let's do some manly-man programming and get this done," what are these women supposed to think?
So if your dev team consisted of a mix of men and women (not even counting if anyone identified as neither or somewhere in between), you'd still say "Let's put in some manly-man programming time" to them?
What if your dev team consisted of just one employee, a woman? Would you still tell her to put in her manly-man programming time? I'm having trouble seeing it. "Jane, it's crunch time. Can you man up and put in some manly-man programming time this weekend?"
I'm sure the old people I know who still refer to black folks as "negros" don't mean anything by it. I also bet the people who throw around "gay" as a generic pejorative aren't thinking of actual gay people when they use the word as an insult. That doesn't make either one acceptable here in the 2010s.
Same with telling a woman that doing something "manly-man" style is doing it skillfully.
And even if you know it's going to be taken as humorous, let me give you a hint: it's not very funny. It's just not very good as humor. There is much better material out there if you're going for a joke.
I am black and would not be offended if someone referred to me as a negro, if they mean no offense, then I take no offense.
I've been referred to as African American, Afro American, colored, person of color, black, negro, etc. It makes no difference to me personally. Unless intended otherwise, it's just a point of reference.
Would you say that your personal experience is generalizable to many/most people of color?
If, say, someone from another company who's visited your offices for a day later refers to you as "that negro in product development," would it be typical that other people of color would take no offense at that use of language?
I'm curious about it. I don't have that lived-in experience, so all I can do to understand is ask and listen.
"not so delicate that they would need to be handled with kid gloves."
See... it's the little things like this. I am pretty sure that was not your intention, but please do know that turns of phrases like that hurt a little, and exclude a little.
To see what I mean, s/kid/jew/ or s/kid/white/ or some other category and see how it reads.
You're sitting in a conference room full of women who are developers, and you start saying, "So let's do some manly-man programming and get this done," what are these women supposed to think?