In my opinion you can't have benevolent sexism without negative sexism. Both should be equally eradicated.
Personally I try to be very kind to anybody, because I believe this is how things should be.
On the other hand, I noticed that sometimes I "hold back" because the other person is a young woman...
This is true for both strangers and colleagues.
Sadly I can cite a few instances were a woman was visibly annoyed because she thought I was treating her differently than I would have otherwise (it's even worse if they're attractive).
I understand that this is because of what women have to go through, but from my own point of view, it's rather annoying.
Last week my hospital's research lab got two new PhD students and I showed them around and told them I was available in case they needed something. The woman quickly managed to casually slip the fact that she was married in the conversation (a bit abruptly too)... And I hate when they do that, setting boundaries even though I couldn't care less about going out with them.
The guy, on the other hand, he accepted anything I could offer without blinking... He even accepted I'd teach him about some of the devices we use.
So, again I understand why this has come to be. But I can't help personally hating the fact that other people assume something about me just because I'm a man and she's a woman.
My SO uses this kind of tactic only once it's extremely obvious the guy is interested (i.e., asking for the phone number, social media, or being downright obnoxious)... Never as a pre-emptive strike.
Thankfully in my profession I work in a context where being extra-kind with patients (without being annoying or infantilizing them) is expected.