Ok, perhaps I am not phrasing it correctly. Dean, especially and Sam tend to treat women with respect who have earned it or who won't except anything else.
They both dismissed Jo until she showed that she had earned respect. Ellen's immediate authority helped her get respect right from the get go.
Missouri, by sure force of personality made sure Dean showed her respect, he didn't just give it to her.
With Meg, Dean didn't respect her, she was just snother women he wanted ti spread her legs for Sam, until he knew something was up. Sam did because he released something was up. And this is when they thought she was just a human.
We have had Dean treat many women has just a sex object for himself or for Sam, especially when he was trying to get Sam laid.
They absolutely can treat women as a serious threat (well you could certainly argue there are bits wi Bela we they didn't), but after a couple episode they treated the character how they should have after the first encounter.
We have seen Dean being dismissive of women, as he sees them as damsels in distress (a lot more in season one). Of course, also in fairness the show does put many a women in the role of damsel in distress.
But from the get go, I never saw any real attitude about women being shown respect, that wasn't shown to be earned ( which they shouldn't have to show you, either sex, not just women) or part of the scam to earn the trust of the locals, in which case I wouldn't call it showing respect, since you are just acting. Also in fairness, especially in the beginning, Dean doesn't treat many people who haven't shown that they earned it, with respect. Men, women, ect.
Not to even mention all the player moves by Dean, hardly respectful (though in fairness there are members of both sex that like that just as part of the game before a hook up). Personally I always, back twenty plus years ago felt respect by someone just coming up and saying I think you look really good, and I would like to take you home and have great sex.
Now Sam has , for most of the series, shown more casual manners in how he treats well everyone (save kids that Dean normally treats fairly well). But was that in truth how he was raised or in did he choose those manners to just act as far away from Dean and John as possible?
Bobby, Bobby, Bobby..... 
Huh. I didn't expect that.
