It looks like it was a bit of a tasteless joke in my opinion, but nothing to create a real witch hunt around.

That doesn't prove its nondescriptiveness. Considering your kneejerk reaction earlier, you're dismissing the term because you don't like it.

And yet that's exactly what happened. Is that the left that you want to associate yourself with? The mob mentality that dictates that they should pounce on and destroy the lives of anyone who says something that's not to their taste? 

As you said yourself, I don't consider myself liberal. I'm quite on the far left on the spectrum. There are more pressing matters in society then tasteless jokes.

I'm dismissing it because it's quite meaningless. And often it's used just to throw everyone under the bus. I see people accusing a "far left regressive left" of something some liberal (which are centre-right to me) newspapers have done. That and it's a term no serious dictionary even carries.

And how were you able to quantify this? I can say that it is often used to criticize leftists who claim they're progressive and liberal, but advocate for illiberal ideas as that is also an equally valid notion.

This is only anectodal evidence and it doesn't offer any quantification that supports your "often" assertion.

Appeal to authority. Whether the term is on a serious dictionary or not does not determine the validity of the term. Your assertion that the term is meaningless is dependent on unquantifiable anecdotes and a logical fallacy.

But people who are far left never claim to be liberal, I only see the term used in a way which doesn't make sense.

And yes, I appeal to authority, what do you suggest we build or language on? Mud? I disavow the fallacy.

And there people who are far left who do claim to be liberal. Again, how do you quantify that there are more far leftists who claim they aren't liberal than those who claim they are?

A fallacy is a fallacy. Appeal to authority is not a valid argument because you are not addressing the merits of the term. If you can't address the merits of the term, then you simply have not made a compelling argument that it is nondescriptive.

If you're a liberal, you're not far left, if you're far left, you'd never claim you'd be a liberal. The only far-left ideology who would incorporate quite some liberal ideas would be left-libertarianism.

An appeal to authority is not valid in a discussion, that's true, but questioning an authority ON language is not debunking a fallacy, it's stupidity.

You still are not addressing the merits of the term which still makes your arugment incredibly weak and intellectually lazy. So no, questioning your logical fallacy is not stupidity because so far, all you have done is ad nauseaum assertion.

The term, Regressive Left, is a term that describes a certain people of the left that claim to be liberal, but supports illiberal ideas, tactics, and policies. Those people can include far leftists, but not all Regressive Leftists are far to the left of the political spectrum. In addition, just because a far leftist is not liberal doesn't change the fact that some claim that they are. Your argument is dependent on the claim that zero far leftists claim that they are liberal, but you lack the quantifiable evidence that supports your claim.