So, here's a tiny lexical question I've noticed for the longest time: (to have/get/give smbdy) the heebie-jeebies is solidly established in American English, probably beyond. The origin is widely traced to the Barney Google comic, e.g. by Michael Quinlon here (also the source of the image) and by some dictionaries. (Sorry for the offensive image, but it was the oldest one I found and the usage warrants illustration.)
Here's the more interesting point: For a while, I've heard people use heebie-jeebie (no -s) as an adjective. A friend of mine refers to academic work he really regards as downright disreputable as "heebie-jeebie shit". I've found enough attestations of it to make clear that it's no fluke ... the usage is out there. Derivationally, it's not hard to understand, I suppose: What looks like a plural noun could easily lose the -s and get zero-derived to an adjective. But I'd completely forgotten but it's actually famously attested (see second picture).