Earlier quoted context omitted.
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?
One would hope they were mature enough to understand an idiom, and not so delicate that they would need to be handled with kid gloves.
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?"