Is it normal for a friend on facebook to only comment on photos in a snide way?

I could copy and paste examples, but then I'd just look like I was paranoid and would bore you.

They leave some nice comments that seem genuinely nice every now and again, but mostly it's either ones that are blatantly meant to be snide or ones that don't come across as snide on the face of it but you can tell are actually intended to be snide.

The last time this happened was 3/4 days ago. They posted a Tweet mentioning me, with the hashtag #schoolmemories and mentioning a bad habit I used to have.

I'd wished them a happy birthday on the first day of the month and not received even a Like from them (I think it was the same case last year), then tried calling them out for the Tweet by writing one mentioning them and something they'd said/done.
I realise now that this was a bad way to call them out for it, but it made sense to me at the time.

Me: You're welcome!

Glad you appreciated the comment enough to write a Tweet about a habit that I had TEN YEARS AGO.
Them: I didn't expect that sort of response - It wasn't meant in a harsh way at all, you read it wrong. It was a school memory and I thought you'd see the funny side of it.
Me: Sorry [Thinking: But you *do* bring it up every time you mention a memory of what I was like in school.]

We were - so I thought - close friends in high school, but there have always been things she's said or done that could be interpreted as being all in good fun, but still feel like they could be some form of low-level bullying.

I won't go into much more detail here, but we had a pretty big fallout in January 2010. I have made no effort to keep in touch with her and let her do the leg-work.
She flakes on a mutual friend of ours at least 80% of the time and - despite, or even because of, having Crouzon Syndrome - takes A LOT of care over her appearance. She makes comments about my outfit or hair every single time I see her. I have has many related nicknames e.g. Paul (for having hair cut in a top-heavy style, a bit like the Beatle), Tipp-ex (for wearing white liquid eyeliner).

I'm getting myself all psyched up for bringing her down a notch or two at a school fayre next weekend, but I know that I would be too scared to do such a thing in real life, whether I was with anybody else or not (And may not do it anyway, just to not ruin her day).

I feel like I NEED to do something just to put her in her place and I hate feeling like I can't do anything.