Q&A: What is the mystery in Genesis 1:1?What are some examples of Hebrew slang and idioms?

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.