Kiffer is an essential French slang verb meaning “to like” or “to enjoy”. It comes from Arabic and is commonly used among young people in France.
kiffer
to like (slang)

Example sentences
For this first sentence, ouais is slang for “yes” and equates to “yeah”.
Tu kiffes ton prof de français ? – Ouais ! Il est sympa !
You like your French teacher? Yeah, he’s cool!
For this second sentence, the adverb trop means “too” or “too much”. But, in this context is slang and a synonym for très (very).
La vérité, c’est que je kiffe mon boulot. Mon patron est trop cool !
The truth is that I love my work. My boss is very cool.
C’était une bonne fête. J’ai kiffé.
It was a good party. I enjoyed myself.
Word origin
The Modern French slang verb kiffer comes from kif (pleasure, fun) in Arabic.