Insidious ageism gets on my tits, as well as the obvious stuff.
I've been following a topic, whereby a Grandmother posted on a thread , saying she wasn't sure about gelling hands, when visiting a newborn and is this normal to expect the grandparents to do this..
Most of the posters assumed she was a grandmother (a woman) and tore her a new one - obviously in their minds, she was an interfering old woman.
But, interestingly enough, as soon as the poster revealed her self to be a Grandfather, which was about 6 pages in......
all of a sudden the whole tone changed and became much friendlieronce the posters realized it was a man: 
Oh, you do have a point and welcome to mumsnet maybe we've been a bit harsh on you^ pass the sick bucket--
I've noticed this a lot on here and especially in RL:
Women will be really harsh and nasty towards Older women, but can be really nice almost simpering when it comes to Older men.
Are some women programmed(conditioned by society would be a better word) to be nicer to men in general, even older ones? But older women don't get the same respect.
I will never understand it.
Yes, Its definitely a Man's world out there.
And a LOT of ageism comes from Women as well as men, sad to say.