I can see two possible scenarios that might result in this image:
 
1)Our favorite trio of Blank-Flanks are still experimenting with how to get their cutie marks, when they stumble upon “Torture-Technicians”. Outdated though it may be, the rise of new evils might signal a need to return to such cold-blooded methods as Knismesis and Gargalesis… whatever that means.  
Oh. It just means tickling. Well, if anyone is in need of a good laugh, it’s Diamond Tiara, and her simpering sycophant sidekick Silver Spoon. All tied up and nowhere to go, the two trussed-up tyrannical troublemakers are at the mercy of our brave crusaders – dressed for the occasion in garb befitting a game of “Applelooseans and Buffalo”. Alas, someone forgot to bring the feathers. But this problem is quickly resolved, thanks to clever observation, and a 2-1 majority vote.  
Applebloom and Sweetie Belle take turns doing their best to make those bullies pay earn their cutie marks, while Scoots laments that she didn’t earn a “Feather Dispenser” cutie mark for her noble sacrifice to the cause.
 
2)The second option is a bit…more intense…  
“You okay, Scootaloo?”  
“I’m…I’m alright. Just a little bit sore.”  
“There we go. That ought to hold them. My big sister showed me how to make knots that can’t be slipped out of.”  
“Untie us, Blank Flanks! Or you’ll be sorry!”  
“Diamond, maybe we should just calm down. We don’t want to get hurt…”  
“Ya should listen to your friend. We’ve got more than a half mind to pummel ya silly.”  
“HA! If you lay but a single scratch on me, I’ll tell my daddy that it was an apple that marred his daughter’s beautiful figure. He would most definitely not like that, and I’d just hate to see your poor old Granny lose her business thanks to your recklessness.”  
“Why I oughta… no one goes around threathenin’ Granny! I- I’ll wipe that smirk off y’alls face with ma bare hooves…!”  
“Easy Bloom! Do not engage! Do not engage! Rarity talked about how she sees this sort of taunting at fashion shows. If you fight her, you’ve played into her game, and she’ll win.”  
“Yeah Applebloom. It’s fine. Really.”  
“No it’s not fine! She hurt you Scoots. She plucked your feathers! You normally would be the one to jump to action! Ain’t you the least bit angry?”  
“I am, but she’s right. There’s nothing we can do.”  
“I’m glad to see someponies have enough sense to know when to quit. Besides, she wasn’t using those feathers anyway. She can’t even fly! Her orange chicken feathers are only decorative, so they might as well decorate my new gown–Which you’ll be able to see tomorrow at the school dance if you let us go right now.”  
“Shut yer trap, Diamond Tiara.”  
“You’re not taking our friends feathers!”  
“Sweetie Belle. Applebloom. Just give the feathers to her. I can always grow back new ones.”  
“..Hold up a second. ‘Give her the feathers?’ …Scoots, I know just what to do!”  
“Huh?”  
“Yeah! Big Mac used to do it to me all the time when I was real little. It didn’t leave no marks, but it sure was effective as punishment! And if anyone deserves to be punished, it’s Diamond Tiara.”  
“Oh, I get it! Rarity did the same thing to me when I made a mess of her apartment one time. Diamond Tiara will be begging for mercy once we get started.”  
“Plus, she won’t be telling no sob stories ‘less she wants all of Ponyville to know how she can’t handle such a childish punishment. And Filthy Rich wont know about it since we won’t leave bruises!”  
“What are you blank flanks talking about?! And why aren’t you untying us?”  
“Do you really think it’ll work, guys? I mean, I don’t know…”  
“It’s your call Scootaloo. They are your feathers after all. You should decide what they get used for; not us, not them, not anypony else.”  
“…I’m in. Let’s make those bullies pay.”  
“Thats the spirit!”  
“Then I reckon it’s high time we earn our cutie marks as…”  
“CUTIE MARK CRUSADER TICKLE TORTURERS!”

They are just going to tickle their captives senseless until they beg for mercy, apologize for being mean and promise to be nice from now on.  
And then they will tickle them a few hours longer to get back at their tormentors and to make sure they really learned their lesson.

Scootaloo: “I can’t believe I’m saying this, but next time, I’m with Diamond.”

Awwww! That’s such a cute and funny picture!  
Almost…poor Scootaloo!

Prepare yourselves.  

Placeholder is a god amongst men.

@anonymouspegasus
 
It was for a worthy cause. =P

.

@someguy111  
The hard part of a hoof is like one big toenail going around the front, they’re softer behind that, so maybe. Cartoon hooves are definitely ticklish though.

The Laughs of the Mohicans

Revenge sweeter than a cupcake.

@anonymouspegasus  
It’s not like she was going to use her wings anyways.

Scootaloo debates the necessity of this activity.

Not enough feathers. It needs to be a full-body tickling experience.

hooves are ticklish?