So a friend of mine moved here earlier this year, he already speaks decent German and a group of us were eating pizza and drinking beer one evening and discussing the differences in Swiss German compared to High German for his benefit.
He was getting most of it but he said one thing that really puzzles him about the Swiss in Zürich is why when they enter a room they say "Hello with one hand". We were all clearly puzzled, I for one was thinking I do the same, I mean I shake hands with one hand - obviously, but that wasn't what he was referring to.
He elaborated "No, why do they always say "Gruezi mit ein Hand?""
Cue puzzled silence for a couple of seconds followed by roaring side splitting laughter (you may have to say it a couple of times to get it )
Indeed. It is an old Swiss custom originating in the city of Bitte Nicht Einsteigen which is also famous, incidentally, for the number of trains serving it. There, one hand is reserved for bodily hygiene purposes and is generally not offered for shaking.