Re: You do know it's the 21st century don't you
is just another acidic drip which make women feel uncomfortable in our tech communities.
Do you actually work in the sector?
I know many women who work in tech, and who have a sense of humour. I can't say I know any who'd be put off by a "blonde/Essex" joke.
Some might be put off by the tired old stereotype/trope that we need to make some sort of effort to 'attract' them to jobs that they largely aren't actually interested in (women who want to be engineers become engineers, those who don't, don't).
If women are feeling uncomfortable around you, then perhaps it's because you're trying too hard to treat them as something different. Treat them as an equal part of the team, as a person, not as a woman or some precious fragile thing that'll break if some complete stranger says something on some random forum.
Whether it's been farming, demolition, engineering or automotive work every women I've met in those fields has wanted and expected to be treated as any other member of the team, and all have resented any form of 'special treatment' because they're female. I can only speak for my experience of course, and I know there are women out there who consider men to be sexist pigs if we don't treat them differently, but most just want to be part of the team, face the same expectations, and have the same opportunities (both social and job advancement).
To act differently because there are (or might be) women around is to act in a sexist and condescending manner towards women.