Those are two very different things.
Hebrew slang is predominantly Palestinian Arabic, or derivations thereof—e.g. mastul מסטול (stoned, zonked), ahabal אהבל (imbecile), dir balak דיר בּאלאכּ (God help you [if you do this]), saḥbak סחבק (close friend), fadiḥah פדיחה (embarrassing mistake, booboo), etc.
Hebrew idioms are predominantly literary and usually of biblical or Talmudic origin—e.g.:
- kitmol shilshom לא כתמול שלשום(‘like yesterday [and] day before yesterday’ = as in the past)
- lo ketza’aqata לא כצעקתא ( not all it’s cracked up to be)
- lelo k’ḥal usraq ללא כחל ושרק (unambiguously).
However, there is a growing number of homegrown Hebrew expressions that have emerged in the modern era, espeically in recent decades, and have entered common parlance, such as:
- al hapanim על הפנים (‘on the face’): face-palmingly bad
- ain matzav אין מצב (‘there is no situation’): no way, that isn’t going to happen.
- sof haderekh סוף הדרך (‘end of the road’): excellent, superb.
Then there’s a whole lexicon of army slang and expressions, which is a tome in itself. Most of it is acronyms of expressions, e.g. shavuz שבו”ז (short for shvur-zayin, lit. ‘broken penis’ = ‘had it up to here’), but some are kept as is, like she’elat kitbeg שאלת קיטבג (‘kitbag question’ = a stupid question that makes the situation worse).
Entire books can be written on each of these, so a blog post can only provide the briefest of samples.