nur Bahnhof verstehen

Etymology
Earlier 20th century. lit. 'to understand only train station'.

According to some sources (e.g. ) from WWI military slang. For front soldiers, would have been synonymous with furlough or relocation to the hinterland, so the phrase would originally have meant “to understand only what one wants to hear”, “not to pay attention”. What may corroborate this theory is the variant.

Other suggested theories:
 * Translations of "train station" would be one of the most important words for international travellers, especially in the era before widespread air travel, and phrases such as "Where is the train station?" appear in all phrasebooks. A visitor to a foreign country who did not speak any other words of the local language would still likely know the equivalent of Bahnhof.
 * A train station is a noisy, hectic place with unintelligible announcements etc.

Verb

 * 1)  to understand nothing at all
 * 2)  to deliberately not pay attention to a conversation