¿Cuál es el vino más amargo? (What’s the most bitter wine?)
Vino mi suegra. (When my mother-in-law came to town.)
Of course, in English, this doesn’t make much sense. That’s because it’s playing on the noun vino and the verb vino. The noun vino means “wine” and the verb vino (the 3rd person preterite conjugation of venir) means “he/she came.” Another way you could translate this into English is like this:
¿Cuál es el vino más amargo? (What is the most bitter wine?)
Vino mi suegra. (I whine bitterly when my mother-in-law comes to town.)
This translation really helps you see how the joke would work in English.