Rainbow Dash is Super (Thanks for Asking!)
Music: I'm Super from South Park - Bigger, Longer, & Uncut
Note: This PMV is for comedic purposes only and shouldn't be taken too seriously.
There's a clashing aspect to this because Big Gay Al's stage persona is gay in a camp, feminine way, whereas Dash is exceedingly tomboyish. Even with 100+ episodes it was difficult finding clips of her acting both feminine and happy. She's mostly fem while fan girling or babying Tank.
As for the old "lol Dash is a lesbo" meme, I'm pretty sure it started way back when just because of the rainbow hair. AJ might be even more butch but "lol AJ is a lesbo" isn't used as a punchline. Shrug.