Sometimes there are double standards because the circumstances are different.
Take the "Twilight Moms" for example - crazy, yes I think so, and they have terrible taste to think that Twilight is anything like a real vampire story, but that's neither here nor there - they are moms. Moms are supposed to be involved in the kids stuff, do the soccer practice yadda yadda, if they have daughters they're going to be hit with the girlie slumber party repeatedly and expected (generalizing here people, very broadly, stay with me) by their husbands to deal with the crowd of girls and by their daughters to hopefully not be super embarrassingly OLD and uptight.
So... in that weirdo chemistry lab you get aberrations like Twilight Moms and Bieber moms and all this other - mentally we aren't as elastic as we'd like to be, and if you go too much into your "mom of teen daughters" role to the "not being old" side - you are going to try so hard to be cool that you end up being... well, not. It happens.
Dads - if you want to look at the other side of the double standard here - are not (generally, again very broadly speaking here) expected to know the singers his daughter is into has a new boyfriend this week or was on the cover of Teen magazine last week with so-and-so but now they found her in a closet with her best-friend's man and it's such a scandal! They are also not usually tapped to be the one to chaperone such outings as concerts with a group of young girls - sometimes just BECAUSE it looks "bad" to have 5 teenage girls with a middle aged man, even if he the father of one of them, which is just plain wrong on society for being so paranoid and ready to think the worst - because, traditionally (and again people, generally and broadly!) the dad is the one paying for the concert tickets to buy the privilege of NOT going and being tortured with an evening of screaming girl-children when he could be home relaxing.
Also, boy children (including teenagers) are not encouraged to get as publicly excited about things, where girls are often encouraged to be as openly emotional as they want to be. So you get a big difference there too - between men and women of all ages and their public displays of enthusiasm.