Just when the ticklee is bound and gagged, and is unable to stop the tickling, that's really hot to me

Asleep on the bed, very gently tickling ̶m̶y̶ their bare soles to wake them up~

ffffffffff, sleep tickling was gonna be one of my answers. Teasing unconscious feet poking out of blankets, making the dry cool sole tremble and twitch. Perhaps gradually waking the tickled one up as you said~ <3

Sleepy tickles are definitely a favourite of mine. Irl fantasy too... For both sides~

Same here. They can be pretty nice.

Cleaning with horse brushes

As the aftermath of accident/chaos like in mouse trouble, market crash or fast food to name a few hehe xP

=P Poor sap trapped like a bridge. Straddling them and lightly tickling their pits

When the tickler is as small as a mouse (or better yet, IS a mouse) and the victim is asleep with their paws fully exposed.

I'd say when the ticklee has a particularly cocky attitude and tickling is a way to humble them down :P

One where a character is placed on a rack and tickled. Bonus if goats are licking

That's a hard one!!!
But, at very least ONE of my favorite all-time scenarios is when a foot is completely trapped somewhere, one way or another. And somebody comparatively much much smaller comes in to wreak havoc on the exposed fragile sole~ <3 <3 <3
A little creature only as large as the foot's arch and heel, tickling its sole. Tormenting it inside of a wall, or threatening the tickled in some way~

as long as their feet are targeted and they're not gagged

Raspberries are super cute.

Using science. XD

Either a renfaire or a farm. Being in elaborate stocks like a box with your head and hands sticking out of the top and your feet sticking out forward. Or sometimes stocks with the feet close together and the hands spread apart, all limbs elevated a bit, of course.

-Stocks, either toetied or not.
-Hunks getting destroyed by tickling has layers of irony I find delicious.
-Tickling as punishment for certain mischievous attitudes (having stinky feet, doing something wrong...)

The list is long and this is just the tip of the iceberg.

I love anything that leans more into the torture side of tickling. I love interrogations, I love punishments, I love situations where the victim is screaming and pleading for it to stop! There's a lot of specific scenarios I could detail, but they all generally fall under the same category of "tickling as a form of a torture".

Lying in bed while their feet are exposed and are tickled awake.

Oh I can't pick just one. Buried in the sand, or stuck in a box with their feet out...the trophy stocks, those are always fantastic...oh! And the kind of scenario where they're dangling off a rope or ledge by their foot and getting tickled on said foot (or feet). I can't just choose one.

Having them bound in a straitjacket stuck in a padded room while either a "doctor" or a tickle machine is going to work on their soles.

Do we need to say just one?

Classic renaissance fair, or some festival of sorts that has foot stocks or some other kind of way to get someone into a situation where they get tickled in public. Could be a renaissance fair, or a "demonstration" at a museum, or at some other kind of carnival.

There is a certain scenario I really like, it's when the ticklee is holding something heavy, with its arms above its head, and the tickler is taking the chance to tickle him. Can be peril or not, depends on the context.

One example would be the scene with King Louie on The Jungle Book. Of course, this works mostly with strong or muscular ticklees.

Interrogation scenarios have really been growing on me

Stuck in a perilous situation (such as having to stay balanced or hold onto something with their feet) where succumbing to the tickles would result in becoming a helpless victim to even more intense tickles (or some other kinky scenario that is partially undesired)

There is the classic of the character being tied up or restrained another way and having their feet tickled.

Those "don't laugh, don't even make a peep, or else [whatever consequence]~", whether that's the powerful prowling tickle monster being alerted to them and their tormentor's presence, or an alarm being tripped, or...

Moments where a noise is inevitable, and the method of drawing it out is all but immobile~