some time ago, may be 150, 200 or 300 zears, ago, anyway, before the modern times of running water from a tap, you could only get fresh, drinking water in Hamburg from the water carriers, who carried two huge buckets of water hanging from a yoke carried on their shoulders. One became famous, Mr. Hummel, because the kids were teasing him, calling out "Hummel Hummel!" Hummel is the German for bumble bee, by the way. I do not know whether that has anything to do with the teasing, but I can imagine it would...
To show his annoyance, he would reply to "Hummel Hummel" with "Mors Mors", which is basically shorthand for "Kiss my arse".
Nowadays, the car registration HH-MM, followed by any number, is still quite popular amongst many Hamburgers. If you see a Hamburger citizen (distinguished looking, intelligent, tall, suave, debonnair etc., and an HH number plate) call out "Hummel Hummel" (the u sounds like oo in doomsday, but short...) , you might get an appropriate reply from a real Hamburger, if he finds that you are not a Hamburger yourself. .