It all started with a question.
Bilbo was naturally bewildered when the younger of Thorin's nephews approached him, mischief obvious in his eyes.
"Well, some hobbits, of course. I mean...I imagine it varies among dwarves as well?" Bilbo responded once he'd overcome the initial confusion.
"True enough," Kili grinned. "I guess a better question would be, are you ticklish, Mr. Boggins?"
The last part was uttered jokingly, as the dwarven prince, having long learned Bilbo's actual name, continued to use the misnomer simply for the amusement of seeing the hobbit's look of exasperation.
Still, Bilbo did not concern himself with the name on this occasion, having instinctively tensed up at the new question.
"O-of course not!" he sputtered, only to internally ridicule himself for sounding so anxious. He quickly composed himself, trying to save face. "What a silly thing to ask. Now is that all, Kili?"
"Sure, sure. I was just curious," the young dwarf grinned innocently...a bit too innocently.
"Well...alright then.. Goodnight, I suppose..."
Still suspicious, Bilbo cautiously turned to walk away.
And the matter was dropped, just like that.
It was not until quite a bit farther into their journey, long after Bilbo had forgotten the peculiar conversation, that Kili struck.
After what resembled an eternity in the wilderness, the company finally found proper rest at an inn. It wasn't the most high class of establishments, but there were warm beds, decent meals, and a roof (albeit a creaky one) above their heads. Grateful for the shelter, everyone took the night to relax.
Bilbo had been harmlessly puffing on his pipe by the fire, minding his own business, when Kili approached him in the same manner as before.
"...Why are you grinning at me like that?"
"Do you remember what I asked you about the last time we had the chance to chat like this?"
Bilbo looked puzzled, staring at Kili, uncomprehending.
Naturally, he never got to finish his sentence.
Before he could even think about defending himself, Kili pounced, hands immediately targeting wherever they could.
There was no strategy or pattern to Kili's attack; he was simply tickling anywhere and everywhere he could reach, scratching and digging and wiggling his fingers wildly through the fabric of Bilbo's clothes.
Inefficient though it may have been, it was enough to get Bilbo squirming and, despite his best efforts to keep quiet, laughing.
"K-Kili! Stahahap!" he demanded, though it was near impossible to sound serious while trying (and failing) to fight back giggles.
Unsurprisingly, Kili ignored him, continuing to tickle the defenseless hobbit with glee. He was relentless, going from the ribs down to Bilbo's sides, and when given the opportunity under his arms.
Bilbo flailed, trying to block Kili's hands with his arms, but it proved futile when Kili simply switched targets whenever he managed to shield a ticklish spot.
However, it wasn't until Kili tried tickling Bilbo's stomach that he truly earned a strong reaction.
"G-GahahHAHAHA! NOHOHO! NOHOHOT THEHERE!"
Bilbo bucked, nearly throwing Kili off of him, but no such luck.
"Woah! Found a sweet spot, did I?" The dwarf prince held on, fingers mercilessly jabbing at the hobbit's belly. "And you said you weren't ticklish! It's not nice to lie to your friends, Bilbo!"
Bilbo squirmed, laughing madly as the torment continued. His movements shifted his shirt upwards, and soon enough Kili found access to bare skin, which he exploited with wicked delight.
Kili poked and prodded and tickled and teased, Bilbo unable to do anything but shriek and squeal as the playful torture went on. Though in reality it had likely only been a few minutes, to the hobbit it felt like hours since the tickling had begun. He couldn't think, he couldn't escape, and he could barely even breathe. Unfortunately, there seemed to be no end in sight. And then...
"...What are you doing to Bilbo?"
And then it stopped, Kili suddenly scrambling off of him.
From the doorway, Fili looked skeptical.
A moment passed in silence as the brothers held each other's gaze.
"You know," Fili finally spoke, apparently addressing Kili, though his words suggested otherwise. "You really shouldn't be taking advantage of other people's weaknesses when you've got it much worse."
The smile dropped off Kili's face as Bilbo perked up.
"Anyway, I'll call you two later when it's time for supper. Until then..." Fili headed for the door, but not before throwing a few parting words over his shoulder.
(And then Bilbo pounced on Kili and tickled him in revenge, as Kili cried out in anguished laughter, bemoaning the fact that his dear brother betrayed him to a hobbit. The end. XP)