1. German idioms deutschen idiomen
Raucht Ihnen der Kopf
(does your head smoke)
when studying German?

2. Idioms
Idioms are phrases or expressions that are unique to a particular language. Defined by the American Heritage Dictionary as “A speech form or an expression of a given language that is peculiar to itself grammatically or cannot be understood from the individual meanings of its elements,” idioms are key to understanding the soul of a language. Idioms point to a shared experience and culture between speakers of the same language. Idioms and other similar colloquial phrases spice up a language by giving it much of its vibrancy and texture. The German language is rich in idioms.
At first, understanding German idioms can be confusing for non-native speakers, especially students. Looking up the individual words that make up an idiomatic expression in a German to English dictionary will confound the student as the words on their own won't make any sense, the entire phrase has to be taken into account when dealing with idioms. Because of this, students of the German language must study idioms in the same way as they do vocabulary. Baseline knowledge is required when dealing with idioms in any language, this knowledge cannot be had intuitively and can only come from study and experience speaking the language.

3. Hals und Beinbruch! Literally: neck and leg break
Figuratively: Break a leg! (an ironic expression wishing good luck)
Origins: Old superstition held that wicked spirits were irresistibly drawn by well-wishing, as it presented them w/ opportunity to cause upset. To trick the spirits, people wished one another the opposite of what was really desired.

4. Hals über Kopf
Literally: neck over head
Figuratively: in a mad rush

5. Jmdm ein Dorn im Auge sein
Literally: to be a thorn in someone’s eye
Figuratively: to be a thorn in someone’s side

6. nicht in ihrer Haut stecken wollen
Literally: not to want to be stuck in her skin
Figuratively: wouldn’t want to be stuck in her shoes

7. sich keine grauen Haare über etwas wachsen lassen
Literally: not let any gray hairs grow over something
Figuratively: not to worry

8. Vier Augen sehen mehr als zwei
Literally: Four eyes see better than two
Figuratively: Two heads are better than one

9. weder Hand noch Fuß haben
To have neither hand nor foot
To make no sense at all

10. wo der Kaiser zu Fuß hingeht
Where the emperor goes on foot
The smallest room in the place, normally the loo
EUPHEMISMS for die Toilette/das Klo/das WC or "I gotta go" include: "das stille Örtchen," "wo der König allein hingeht," "ich muss mal," "ich muss wohin."

11. Das liegt auf der Hand
That lies on the hand
That is obvious! (Duh)

12. etwas mit den Füßen treten
To step on something with the feet
To treat something with contempt
Related: jemanden mit den Füßen treten
To step on someone with the feet
To walk all over someone

13. etwas auf dem Herzen haben
To have something on the heart
To have something on the mind; to be thinking about something

14. jemandem fällt das Herz in die Hose
Someone’s heart sinks to the pants
To be scared to death
Als es krachte, fiel mir das Herz in die Hose."

15. Mir raucht der Kopf
The head is smoking to me
My head is spinning

16. Wer rastet, der rostet Who rests, rusts Use it or lose it
Related Parody: Wer rast, rostet nicht (who speeds, does not rust)

17. Wer Feuer frißt, scheißt Funken.
Literally: Who eats fire, sh**s sparks
Figuratively: This will come back to haunt you/bite you in the butt
Related Idiom: sich in den Arsch beißen
Ich habe mich in den Arsch/Hintern gebissen. Literally: to bite oneself in the rear Fig.:   I was kicking myself/expression of remorse