Breakdown of Ich missverstehe deinen Ausdruck völlig.
ich
I
deinen
your (informal singular, accusative masculine)
völlig
completely
missverstehen
to misunderstand
Questions & Answers about Ich missverstehe deinen Ausdruck völlig.
Is the prefix miss- in missverstehe separable or inseparable?
It is inseparable. That is why it stays attached to the front of the verb rather than moving to the end of the sentence. You would never say Ich verstehe deinen Ausdruck miss.
How would I say this sentence in the past tense (Perfekt)? Does the miss- prefix take a ge-?
Because miss- is an inseparable prefix, you do not add a ge- to form the past participle. The past tense of this sentence is simply Ich habe deinen Ausdruck völlig missverstanden.
Why is it deinen Ausdruck instead of just dein Ausdruck?
Ausdruck is a masculine noun (der Ausdruck). Since it is the direct object receiving the action of the verb (the thing being misunderstood), it must take the accusative case, which changes dein to deinen.
Does Ausdruck refer to a facial expression or a spoken phrase here?
It can be either! Der Ausdruck is a very versatile word that can mean a facial expression, a spoken phrase or idiom, or even a printed document. In this context, it most likely refers to the way the person phrased their words.