There have been a few low points during the past month, when I have been sitting in darkened rooms listening to comics of varying talent at the Edinburgh Fringe, but the nadir was reached when I was judging the "So You Think You Are Funny" newcomers competition. Miming masturbation and ejaculation over a young woman in the front row, one posh twenty-something male comic gleefully told the audience that they had just witnessed "the death of feminism".

I'm past being shocked when it comes to women being baited by stand-ups, so endemic is it, but this really depressed me. What does it say about our society that this well-educated and no doubt well-brought-up young man thinks that this material is acceptable?

I'm sure, if questioned, he would the use the "it's ironic" defence that comics always use when anyone objects to dodgy or borderline racist, sexist or homophobic material, but I cannot see where the irony lies in such an aggressive act. And I'm certain he wouldn't have dared do that riff with a man.

Maybe he took his cue from the more established comics on the Fringe, for whom rape jokes are de rigueur. American Reginald D Hunter accuses women of "emotional rape" (whatever that may be) in the battle of the sexes; men have the strength to overpower a woman physically, he says, but women can destroy a man by being a shrew. Oh Dr Freud, you should be living at this hour...

The "irony" defence is nonsense, of course. Comedians are really being lazy and base. When it is used properly, irony is a fine tool, not a bludgeon. Intelligent comics use irony to subvert jokes and preconceptions. The joke is on them, and by extension, us the audience, when the penny drops that the comic is saying the complete opposite of what we thought he was about to say.

Two very funny and clever stand-ups, Canadian Pete Johansson and cockney Micky Flanagan, both present themselves as having been lotharios in their youth and have explicit sexual material about their wives. But just as you think they are victimising women, they turn the joke on themselves and they are exposed as foolish oafs rescued by the love of a good woman.

I don't believe the majority of comics are misogynistic – indeed, most agents and publicists in comedy are women and all say how respectful their clients are – so something more calculating must be at play. The foundation of comedy is recognition of shared experience, so these performers must hold a mirror to our sensibilities.

Perhaps today's young comics – nearly all educated and middle-class – assume the battle for equality has been won and they therefore can do crass, sexist material with impunity because, of course, they don't really mean it. But the popularity of their material tells us there is still work to be done.

Once stand-ups like Bernard Manning were ridiculed by a generation of alternative comics proud to call themselves feminist. We have now come full circle. Maybe, as that distasteful young comic said, feminism really is dead because, were Manning still alive, he would go down a storm at the Fringe.