I actually ran into a game where the enemy team was all-AD once, but I didn't know what to have in runes/items to punish them properly for that. I built Ninja Tabi and a GA and then Trinity Force and just that was enough to have them never kill me but I felt inspired by that, to improve on it, to make a build which while dealing absolutely zero damage would make the enemy team absolutely MISERABLE.
What I came up with was the following.
For a full-tank Ashe, run the runes of Grasp of the Undying + Shield Bash + Conditioning + Overgrowth + Overheal + Legend:Bloodline (this gives you shielding + lifesteal); I believe the best runes are adaptive force + armor + health here, though the second health might also be better to be armor.
For items, ninja tabi for movespeed + armor, GA for some attack damage + the revive + the armor, then build into Frozen Heart (the item with the highest armor in the game, 100), then Thornmail (second highest), finishing with Randuin's Omen and Iceborn Gauntlet. Haven't tested out how much health that'll give you and how much armor it'll give you, but against an all-AD team...in theory you should never die.
Obviously, this is still not an optimal build against even an all-AD team because sure, you might never die and be invincible, healing faster than they can deal damage to you...but like, armor penetration/lethality can still hurt you and you deal no damage so it's not like the build is really good. But, in one specific instance of facing an all-AD enemy team, it could be fun to try out.
A similar idea which I've thrown around was based around "how to beat Eve in a 1v1 against her", but works against a full enemy team comp of AP damage dealers. The best I can figure out for that: Aery (the Sorc primary rune) seems like the best primary keystone, with Nullifying Orb as a MUST from the sorc tree--even if you ran something else as the primary tree, Sorcery would need to be the secondary for that rune. I chose Bone Plating + Revitalize as my secondary runes, since it seemed to be decent. Obviously, Adaptive Force + double MR for the flex runes.
As far as items go, the items to build would actually be actual adc situationally-built items for the most part: Merc Treads, Maw of Malmortius, Mercurial Scimitar, Wit's End; these give attack damage, healing, and attack speed, while also having passives which interact with receiving magic damage. Spirit Visage is a good anti-AP/anti-assassin addition to this, which leaves a final item slot for either Banshee's Veil or Adaptive Helm.
So this comp is obviously not an ideal adc build, but it at least deals reasonable dps. Not maxed dps, but okay dps. But the goal here is to do the same as tank-Ashe above does to an all-AD team, against an all-AP team: the goal is not to deal damage as an adc, the goal is to make the enemy team not have a fun time by your absolute refusal to die. Obviously, they have magic penetration items to ruin the build, but if you stack mr faster than they stack magic pen, I think that the damage reduction still can at least partially work.
Like the above, it ONLY works if, SOMEHOW, the entirety of the enemy team has ONE damage profile, this time magic damage rather than physical damage. So it's not something you'd get the chance to build very often at all. And even if you did, it's still a little trollish to build because uh...yeah. Not an optimal adc build, not a build which synergizes well with Ashe.
But while a bit trollish, and making the enemy team miserable, and probably getting your team to call "Ashe, what the hell are you doing?", it's something I can see as being incredibly fun to do if you actually did get the chance to try it out.