@DragonBoi471  
I agree and disagree with you.  
1)There’s no indication on weither or not she had wear a dress at all.  
2)I think the spa thing was literally as said “I hate having ponies touch my hooves” which is true as some people don’t like other touching certain body parts (I don’t like having my neck touch for instance, feels weird)  
3)The swarm thing: wouldn’t that be more of “I hate fashion” and not “I hate all things girly”  
4)event clothing: Even if she did, and if the writers wanted to make a point about that as her preference, then why is it that Rainbow never complains about were dresses when she does?
 
Rainbow doesn’t care for fashion, but that doesn’t mean she can’t get dressed up or that she has a hate streak with “girly” things. Rainbow is just :/ about it really not for not against.

@ColdhardSilver  
Well the reason is that a lot of people think that Rainbow Dash, despite being a masculine tomboy, actually enjoys all this feminine stuff. However, I think that canon states otherwise.  
EXHIBIT A:  
In the S1 episode Swarm of the Century, Dash is seen being a live mannequin for an 18th-century dress Rarity is working on. She later complains that this is “Way too boring”, and that she would rather be out flying.  
EXHIBIT B:  
In the S2 episode Ponyville Confidental, Rainbow Dash visits the Ponyville Spa but refuses to have a pedicure because she “Doesn’t like ponies touching her hooves.”(It’s also likely that the headline image afterwards was probably fake.)  
Now I know what you guys are probably thinking-“But Rainbow Dash wore a dress to the Gala, the Royal Wedding, and the Corronation.” Well, yes that’s true, but keep in mind that those were formal occasions. In those scenarios, Rainbow Dash has no choice but to wear such a girly outfit.  
Anyway, that’s my two cents.  
_{Sorry if this comment was too long.}

@DragonBoi471  
but isn’t rainbow rejecting the dress because it is messing with her flying (hence the crashing into a roof right after) what does that have to do with her feminine tastes?

Next time I encounter somepony who says that RD actually enjoys girly stuff, I’m just gonna link them to this image.

@Mellow91
 
Oh, I agree with that. But it’s still a cool looking dress.
 
@Potatoguy
 
Maybe someone can draw RD doing a Tea Ceremony in this outfit.

I’m waiting for a humanized version.

Now I want to see fanart of her ripping that dress off a la Ryuko.

@Inkan1969  
It still doesn’t beat her gala dress by any mile! :)

To be honest, that dress actually looks pretty good on her.

You look nice in that dress, Dashie!

Like if you put little shoes on a cat.

Flying in a dress must really mess up balance.

@JP  
If you ask me, I don’t think that dress is her colour.

CLOTHES BEAM!  
That is easily my most mediocre spell.

So they finally made the joke. Or did they already back in S1? Someone help reminding me please?

That actually looks quite nice on you, Dashie.

Looks like she’s wearing a kimono.

Oh stop it Dashie.  
You look fabulous.

might seem harmless but there is no way to get them off without a cutting tool.