Which unit(s) don't you want to have as pitybreaker?

[Cornguy]

Luke and Faye, stay away. How I've pulled two of each of you off-focus I don't know, but BLyn already has a FS, and Luke doesn't give me anything I need. Probably wouldn't be thrilled to see Mist, but I don't have one yet, so it wouldn't be the worst.

[Fabulously Olivier]

Red: Gray, Soleil, Luke, Young Tiki

Blue: Tailtiu, L'Arachel

Green: Rhajat, 

Colorless: Faye, Elise (my most disliked character in the entire franchise)

Other: Almost every seasonal unit outside of performing arts.

[nirvanafan]

Units I have but do not plan to level up or some of the alts for characters I already have (ex. I am cool only having Possessed Takumi & do not really want normal Takumi).

[wheelsonfire]

Any unit that I've gotten before, honestly... I don't use the merge mechanic, due to having a lot of teams at once, and needing the extra units... Furthermore, a lot of the events don't allow duplicates, so the units are not all that helpful... I've gotten lucky with 5 star pretty breakers, but it hasn't been useful that a lot of the units have been downgraded to three or four stars are ones I don't need/want...

[Legend_of_Zelia]

Any unit I've gotten before except Azura and units you can easily get as *4 and *3. 
Also I don't want anymore Brave units. While B!Lyn is a good overused arena unit, she's kinda of a cock blocker, I had gotten three of her as pity breakers, so haha, no more of her... ^^'

[Charmeleonbrah]

Maria and Lachesis have been the worst of the pity breakers for me. The former showed up at a 5% rate on the Bunny Heroes banner (instead of Kagero)

[SniperGYS]

Anyone I don't like

[Alexmender]

Basically Mist is the only unit I don't want to see ever (and Nanna will join her soon because both suck) but for the sake of putting some others that would end as nothing but fodder which isn't even unique to them: 

Red: Leo, Karel, Gray.

Blue: Shiro.

Not that many units, that's because most of the 5* units are either good investments or have at least 1 nice skill to give.

[r_n]

In general, I'd like new units rather than repeats of those I already had, but thankfully the culling helped a lot

Aside from that, some specifics are

Red: Eldigan, Karel, Ryoma, Sanaki because Fury, Desperation,Vantage and TA area all super common as-is. I'll merge them but I'd rather get others, you know?
Soleil because I actually have 2 spares of her and that's about all I'll need so far as Firesweep Swords go.
Everyone else I either don't have or offer good stuff (Swift Sparrow, Quick Riposte, Aether, Flier Formation or DB3*)

Blue: Basically just Azura. I already have a spare for her and I've still not found a user for her sapphire lance. Olwen because she has nothing I'd mulch her for and same for Ninian who I pulled thrice....

Green:  Julia. She offers me nothing but merges. Sonya I'd prefer not getting multiples of, but at least she has res ploy.

Colorless: Jaffar. Everyone else I either don't have or they've got coveted skills. I mean Life & Death 3 is nice, I guess, but if I'm pulling on colorless I'm bound to get more Sothes so...

*I don't pull on colorless that often so I'm usually scrounging around for sources of DB3