[GA] Boss issuing what feels like unjustified write-up

Hey all,

So my coworker called me after hours after a 3 hour evaluation to just vent. We are usually paired up as a team, and we get on really well, so I was okay with that. I heard him out, and even commiserated regarding our boss continuously failing to deliver on something he said he would deliver. My coworker suggested our boss did not actually know how to approach the delivery, hence ongoing delays. I agreed it was possible.

There was some shit-talking, as generally might happen after hours between work buddies. Shooting the shit, etc etc. Moreso about a coworker than boss, actually. My coworker has an ongoing feud. I don't like the other dude, as he only ever shit-talks me (grandstanding and boasting moreso, not truly personal attacks) and seems to leave everyone else alone, and his arrogance is just kind of insufferable. I can work with the guy, and I think things are improving (he seems to be fine one-on-one anyway), but I do not like him.

Well. My coworker pocket dialed our boss at the same time, who heard all of it.

Now I get it, his feelings are hurt, and he did not enjoy hearing that. But he is writing us up for inappropriate behavior (okay, I can see that) and insubordination. They latter rubs me the wrong way. Our boss has repeatedly failed to deliver, we had asked him multiple times, and subsequently we were venting. I get it does not feel great to hear your team questions your abilities, but this feels like revenge more than appropriate managerial behavior.

Anyway, I have to sign the write-up, and I am struggling. If I sign it, is it going to cause issues at future jobs? I assume if I don't, I'll be fired. I already would not use this boss for a LoR just because I feel like he holds everything against me on some secret tally sheet I can never escape and he pulls it out whenever he's upset. When I received a work phone initially, I was admittedly not the best at remembering it, and he lists that as a flaw of mine to other people. It has easily been a year since that has occurred, but he's still bringing it up. I can't escape his negative opinions of me, though he acts like he's forgiven me my transgressions. So I fear using him as a reference would mean he'd paint a less than positive picture of me.

Anyway, any advice? Should I just sign it and deal?