This headcanon’s peggie rumps are truly blessed with an abundance of coverage & signal capability.

From source:
 
Twilight Sparkle: (approaches the Pegasus) Hey, Rainbow! Can I ask you som-  
Rainbow Dash: (turns round to face Twilight) Oh, hey Twi!  
Twilight Sparkle: My, you’re simply beautiful! I never thought you would have let Rarity touch your mane!  
Rainbow Dash: Eh, yeah, I gotta say I’m, like, 15% cooler thanks to her. But that was my idea.  
Twilight Sparkle: Actually, I never even thought you would have ever combed your mane…  
Rainbow Dash: Uh, okay, now you can-  
Twilight Sparkle: On second thought, I’d never imagined you had a brush in your house!  
Rainbow Dash: Wow, you’re great at offending ponies, you know?  
Twilight Sparkle: Yeah, sorry. It’s just, I mean, you, Rainbow Dash, hav-  
Rainbow Dash: (puts a hoof on her friend’s mouth) I got it.  
Twilight Sparkle: What about your dress? I’ve heard Rares say that she had prepared some “divine” gowns for us all.  
Rainbow Dash: Yeah, I’m going to the boutique later. I can’t wait to see what she’s done for me!  
Twilight Sparkle: (giggles) I’m sure you’ll love it. Aaaand… maybe somepony else will, too…  
Rainbow Dash: (blushes) I g-guess…  
Twilight Sparkle: Aw, don’t you worry. Your plan will go perfectly.  
Rainbow Dash: Yeah, now, changing topic… You were saying something before starting to praise how awesome I am. What was it?  
Twilight Sparkle: Oh, uhm, I just wanted you to give me a piece of advice…  
Rainbow Dash: (puts a hoof around her shoulder and tightens the grasp) Oh, dear, little, adorable Twi. You know you can tell me anything. And with anything, I mean anything…  
Twilight Sparkle: Well, it’s just… you know… I-  
Rainbow Dash: Just spit it out!  
Twilight Sparkle: I w-wanted to ask Flash out f-for a date… And… And I just don’t know what to do!  
Rainbow Dash: Ah! (punches her shoulder) You’ve asked just the right pony! He’s a Pegasus, you’re partly Pegasus, and I am a Pegasus! It couldn’t have been better!  
Twilight Sparkle: …Why that?  
Rainbow Dash: ‘Cause I know just everything ‘bout Pegasi behaviour!  
Twilight Sparkle: Do I have to start worrying?  
Rainbow Dash: You can do that later. Now, let me show you what you’ll have to do. (flaps her wings twice then folds them) You have to tell him you are the dominant one, so you have to raise your tail feathers and spread them wide.  
Twilight Sparkle: R-Rainbow, I think that mayb-  
Rainbow Dash: Then, walk toward him lifting your legs slightly more than how you normally do (That’s always to show who’s the boss, remember!) and, as you close the distance, you start to flip your tail a little.  
Twilight Sparkle: Do I have the right to talk here?  
Rainbow Dash: No. Who’s the teacher?  
Twilight Sparkle: Umh, act-  
Rainbow Dash: I am. So listen to me. Now, where were we? Ah, yes, the tail. After that, you walk slowly until your heads are at the same level, and at that moment-  
Twilight Sparkle: I don’t like where this is going…  
Rainbow Dash: And at the moment, you unfold a wing and you caress his cheek, whispering into his ear seductively: “Make me yours”  
Twilight Sparkle: (blushes furiously) WHAT?!  
Rainbow Dash: If you prefer, a little more direct alternative is: “Let’s mate”  
Twilight Sparkle: ARE YOU CRAZY?!  
Rainbow Dash: (nudges her) Admit it, that’s what you’re aiming to…  
Twilight Sparkle: RAINBOW DASH!!  
Rainbow Dash: Don’t lie…  
Twilight Sparkle: Ugh! Why did I ever consider asking you?!  
Rainbow Dash: Your wings are pretty explanatory…  
Twilight Sparkle: And you two stay down! (tries to fold them with her hooves)  
Rainbow Dash: (bursts into laughs) Man, I’d give my left leg to see you doing and saying what I’ve just shown you…  
Twilight Sparkle: I’d never do that!  
Rainbow Dash: I did. It worked with all my ex-coltfriends; every stallion always fell to that scene!  
Twilight Sparkle: You’re such a shameful, reckless panderer!  
Rainbow Dash: (giggles) Well, thank ya, Miss Wings of the Year… (points at Twilight’s wings, wide open once again)  
Twilight Sparkle: UGH! I can’t believe Applejack is able to bear you every single day…  
Rainbow Dash: Aw, she just can’t resist me, that’s different. Now excuse me but I have to go, or Rarity’ll freak out when she notices I’m late. See ya later, colteater…  
Twilight Sparkle: I hate you.