Kopat si vlastní hrob
Literally translating to “to dig one’s own grave,” this idiom is used to describe someone who is doing something that will ultimately be harmful to themselves.
Když Petra neustále odkládala svoji práci, jen si kopala vlastní hrob.

Mít hlavu v oblacích
This expression means “to have one’s head in the clouds,” and is used to describe someone who is not paying attention or has unrealistic ideas.
Martin vždycky sní o cestování vesmírem, opravdu má hlavu v oblacích.

Fakt jo?
Slang for “Really?” It expresses surprise or scepticism and is used much like the English “Seriously?” or “Really?”
Včera jsem potkal celebritu ve městě. – Fakt jo?

Natvrdo
A slang word that translates to “hardcore” or “hard.” It’s often used to describe someone or something that is extreme or intense.
Ten nový učitel je natvrdo, musíme se učit každý den.

Na drátkách
Literally “on wires,” this idiom refers to having a lot of energy or being very alert, often as if one had consumed too much caffeine or is overly excited.
Po té kávě jsem byl celý den na drátkách.

Za studena
When something is done “za studena,” it means it is done without any preparation, or “cold.” It’s akin to the English expression “to do something cold turkey.”
Rozhodl se za studena skončit s kouřením.

Kejchat
A slang verb meaning “to work hard” or “toil away.” It particularly describes laborious work with a sense of difficulty or struggling through it.
Celé odpoledne kejchám na zahradě a připravuji ji na léto.

Jít kolem horké kaše
This idiom, meaning “to beat around the bush,” describes someone who is avoiding getting to the point or addressing the main issue.
Přestaň jít kolem horké kaše a řekni mi, co se stalo.

Mazec
A slang term for something that’s “cool” or “awesome.” Use this word to express appreciation for something that’s impressive or extremely good.
Ten koncert byl fakt mazec!

Jožin z bažin
A funny and nonsensical phrase that comes from a popular Czech song about a fictional swamp creature. It’s often used humorously to refer to an outlandish or peculiar situation or person.
Ten týpek je jako Jožin z bažin, nikdy nevíš, co přijde dál.

Incorporating these idiomatic expressions and slang into your conversation can spice up your language skills and bring you one step closer to sounding like a native Czech speaker. Remember, language is not just about grammar and vocabulary; it’s also about culture and the unique ways that native speakers express themselves. Get out there and start practicing your Czech idioms and slang—your conversations will be all the richer for it!