Stick/stand out as a sore thumb
 

I thought it was "it sticks out as a sore thumb" but I've just heard "it stands out as a sore thumb" in a British reality show. Are both interchangeable? Are both common either side of the pond?

In this case the speaker was talking about a noticeably wrong architectural feature in the room. Does the alternate expression make sense only in a context like this one?

To stick out like a sore thumb is the most common term.
Because stand out and stick out have similar meanings, they are interchangeable.

Like and as are similar too. but like works best as a preposition and is therefore preferable. As is best as a conjunction in this form and it sounds like an overcorrection as many people incorrectly use like as a conjunction which officially it is not.

PS To stand out is usually a positive phrase. Something stands out for excellence
To stick out is always negative.

How about the verb destacar? I am under the impression that it is a positive term. I assume it can be used negatively as well, but I am not sure.

Excellent! Thank you.

I'll try to study that about like and as which seem to be soundless synonyms in my brain (I read or hear "like" and write "as", or vice-versa, without even noticing). Your explanation is very clear and I think I got what you mean: with like it's a comparison or sort of an equivalency; with as it might sound like the sore thumb is the unlikely replacement of what is sticking out had that not been illogical.

About destacar, yes, it's positive or neutral. I would use notarse mucho for defects and llamar la atención for features, but I don't think there's an equivalent expression in Spanish. We tend to use dozen of terms either to describe the visually offending thingy or our actions or reactions in its presence:

for bulky objects: ¡es un mamotreto!
for ugly objects that are indisumulables (tricky to find an English equivalent): ¡es un adefesio!
for things that caught your attention when they shouldn't: "apenas entras se te van los ojos a/hacia..."

indisumulable may translate as unsingular

I can't find dictionary entries nor corpus examples for unsingular, and the few examples in books.google point to it being an antonym of singular.

On the contrary, indisimulable doesn't point to being one of a kind or, on the contrary, a run of the mill item, but to the fact that you wouldn't be able to conceal the indisimulable thing no matter you used the better techniques and efforts, even if you counted with the willing complicity of the observers: the indisimulable thing will continue to stick out like a sore thumb, and the indisimulable feeling will be shown clearly. An indisimulable thing is an elephant in the room.

To stick out/stand out as a sore thumb

Palpario, patente, evidente, palpable, obvio, salta a la vista

Stand out = Poner de relieve, destacar(se), sobresalir.

Gracias. Es raro que en el inglés no conozco y es possible que no existe nungún verbo que equivale to stick out like a sore thumb.
Existe adjective blatant que singifica algo que no se puede esconder.

Right, blatant would be very close translation into English.
Thanks.