Originally Answered:

What expression from your language would English speakers find really funny if translated word for word?

Ah, you remind me of the Golden Treasury of Greek-English expressions: we have not seen him yet, and we have removed him John

I posted an analyses of a few of these on my Greek linguistics blog in 2010: Ἡλληνιστεύκοντος

• Don’t you defecate us you and your cricket: Δεν μας χέζεις εσύ και ο γρύλος σου! = I rebuff your expression of concern. (Actually: Take your car jack and shove it, alluding to an old joke.)
• We have not seen him yet, and we have removed him John: ακόμα δεν τον είδαμε, Γιάννη τον εβγάλαμε. = We rushed to a conclusion. (Actually: We haven’t even seen the baby yet, and we’ve already come up with the name John for it; ‘remove’ = ‘take out, publish’.)
• Eye-removal beats name-removal: Κάλλιο να σου βγει το μάτι παρά το όνομα. = Better your eye be poked out than your reputation.
• Will I extract the snake from the hole; Εγώ θα βγάλω το φίδι από την τρύπα; = It’s a dirty job but someone’s got to do it.
• He doesn’t understand Christ: Δεν καταλαβαίνει Χριστό = He does not understand common sense (Actually: “He doesn’t understand any Christ” = “Christianity” = “what is self evident in our culture”)
• He saw G.I. Christ: Είδε τον Χριστό φαντάρο = He is so terrified, he is hallucinating.

• He cannot crucify girlfriend: Δεν μπορεί να σταυρώσει γκόμενα = He can never get a girlfriend (Actually, “make the sign of the cross over, as a blessing” = “thank his lucky stars that he finally got one”)

There are funnier ones, those are just the ones I’ve published analyses of…