It bugs me when people say “the thing is is that” (if you listen for it, you’ll start hearing it… or maybe that’s something that people only do in my area.) (“What the thing is is that…” is fine. But “the thing is is that…” bugs me.)
Also, “just because <blank> doesn’t mean <blank>.” That sentence structure invites one to take “just because <blank>” as a noun phrase which my brain really doesn’t want to do. Just doesn’t seem right. But that sentence structure is very common.
And I’m not saying there’s anything objectively wrong with either of these. Language is weird and complex and beautiful. It’s just fascinating that some commonly-used linguistic constructions just hit some people wrong sometimes.
Edit: I thought of another one. “As best as I can.” “The best I can” is fine, “as well as I can” is good, and “as best I can” is even fine. But “as best as” hurts.
The thing is is that it’s just a phrase to hold space while you collect your thoughts before you speak. You know you have something worth saying, but may not have organized it into a cohesive sentence/words just yet
The context in which it is used makes sense, but the extra “is” is just there. By all rights it should be ungrammatical, but people pretty frequently have that extra “is”, and I do find it absolutely bizarre how pervasive it is.