Or can it go either way, depending on context, as in the example below?
I have always wondered if the expression “have a thing about” per se can be ambiguous.
(1) I have a thing about skinny jeans. The snug fit throughout my legs makes them look longer and slimmer.
{I **love **skinnies}
(2) I have a thing about skinny jeans. Too tight a fit makes it a real pain to wear them for long hours.
{I **hate **skinnies}
Either way. Context and/or further explication disambiguate.
I can’t recall ever coming across “having a thing about” being a positive. It’s always negative, as far as my internal sense of the language goes.
“I have a thing for” is positive, but I wouldn’t use it for jeans that you would wear yourself. If you say “I have a thing for skinny jeans”, I’d expect that you like to see attractive other people in skinny jeans, not that you like to wear them yourself.
The phrase “having a thing about” is ambiguous. It’s probably more often meant as a negative but not always so.
Yeah, without any further context, I would tend to mentally substitute the phrase “complicated opinion” for “thing” in that expression. 
I agree with Hellestal - Have a thing about is negative; have a thing for is positive.
I have a thing about skinny jeans, but I have a thing for corduroys.
Oh, I see. It now makes me wonder if “I have a thing against” is commonly used as well?
I don’t know about “commonly”. In my neck o’ the woods, the usage seems mostly “thing about x”, and whether it’s a “love thing” or “hate thing” has to be determined by context, tone, or body language.
What a great American phrase, as much ambiguity as you can pack into just a few words.
If that connotation is widely used, it’s not one that I’ve ever paid any attention to. In my experience “have a thing” just means “feel strongly about” and that can be either positive or negative.
I tend to assume positive unless the context tells me otherwise. I think that’s because my first associations for “have a thing” meant some kind of romantic feelings. It wasn’t quite a relationship - maybe just a crush or a hookup (in the days before there was a word for hookups). So a guy might have said “I have a thing for Jennifer” and he probably just meant that he wanted to ask her out, not that they had a definable relationship. It was a while before I remember the phrasing being applied to anything other than people/relationships.
I agree that “have a thing” means “feel strongly about.” Or maybe even more like “I have complicated feelings about.”
It can be more than just like or dislike. You could say “ugh, I have a thing about skinny jeans. I mean I think they make my ass look amazing and I would wear them every day except I can barely breathe when I have them on and I can’t stand the fabric!”
There’s more to that than just loving or hating.
Another example would be “I have a thing about Justin Bieber. I think he’s such an awful person and I hate his hair but boy do I love the way he sings!”
Other people who do not have a “thing” about jeans or Bieber would say maybe they love them, they hate them, or have absolutely no opinion either way.
I would not have expected the feelings of “love” and “hate” to coexist in the phrase “I have a thing about”. :eek:
Have a thing is negative.
Have a thing *for *is positive.
Honestly, it goes either way. The expression is used in both contexts pretty equally in my opinion.
This is also my experience. The latter part of the second paragraph, however, I disagree with - that could go either way, based on context.
I agree. I don’t think I’ve ever head “have a thing about” as positive in the wild. I think people thinking that may be merging “I’m all about” and “have a thing for”.
Also, someone here has a thing for Xenoblade.
Actually, I partially take it back. I don’t think “I have a thing about” is necessarily negative, but I think it’s decidedly non-positive.
Like “I have a thing about piles of stuffed animals. I always get this urge to jump in them and giggle and everybody looks at me all weird.”
I don’t think it’s ever used to describe something purely positive. There always has to be a hint of oddity or quirkiness at least. I’d say it’s roughly synonymous with “I have weird hangups about…”
I think it can be positive.
I could easily hear myself saying “I have a thing about short freckly blonde girls”.
I find the points you have raised interesting. 
Incidentally, to muddle things further (ha-ha), I wonder how “I have a thing **with **something” compares with “I have a thing **about **something”. Some seem to favour “with” over “about”.
when you “have a thing” about something you have a strong opinion.
That opinion could be either way.
Some people have a thing about promptness. They dislike anyone being late (or in principle early).
But that means they are in favor of being on time. So they like one thing and dislike another.
To " have a thing" is to have a strong opinion.