NO reply is usually the BEST reply, when you're dealing with a pesky Borderline.
I used to get viciously attacked for my views and writings on the topic of BPD. It's a waste of time and energy to defend yourself to a Borderline, or try and reason with em.
I see a lot of really intelligent people getting triggered by Borderlines on social media platforms. It can exhaust ya.
Your BEST move, is don't bother dignifying their comments with a reply (no matter WHAT they throw at ya). Borderlines LIVE for attention, regardless of whether it's positive or negative.
I know it's hard to resist having the last word, but the only way you're gonna get under their skin and FESTER there, is to go NO CONTACT. In short, Ignore, ignore, ignore!
Eventually they get tired of knocking on a door that won't open, and they slither off into the night, seldom (if never) to be heard from again.