To add to some of the excellent responses (viewed as a Brit/South African married to a German, who has worked in Germany for a number of years):

• Sleeping on large square pillows that have almost no filling
• Rapping the table top with your knuckles instead of clapping (perhaps more common at a corporate event)
• Calling one another Mr (Herr) - at least until you are formally encouraged to refer to them as ‘du’. Very amusing seeing two younger adults referring to one another as Mr...
• Queuing… may be I have lived in the UK too much, but Germans are appalling in a queue. If you leave the tiniest gap someone will push in… Perhaps Germans need the ordnung of a numbered system…
• The use of English words in a totally German way. The German language has absorbed words like ‘handy’ (a mobile phone) and ‘sport’ (exercise). Germans are a little bemused when English speakers do not understand the useage.
• The apparent enjoyment in drinking horrid, horrid UHT milk. Fresh milk is hard to find in Germany - I guess that long-life UHT milk is just so praktisch.
• Dinner parties - invite someone to dinner at 7pm, and they will expect dinner to be on the table, ready, at 7pm. No small talk before!
• The way that everyone is expected to pay when eating out. You tell the waiter which beer you had, what meal you ate, and pay for that. None of that imprecise, lets split the bill 50:50 or whatever.
• The tradition of watching ‘Dinner for one’ (an old English comedy, no-one in England remembers) on New Years Eve. I mean, it seems much of the country watches it every year on New Years eve!
• The look of horror if someone walks into a sauna with swimming trunks on.
• The anger a cyclist vents if you accidentally walk in the cycle lane.
• Strapping branches of trees to posts in May (to show your love of someone) - ‘Maibaum’. Never forget seeing a whole Birch tree strapped to a lamp post in Cologne once.
• Receiving presents on Christmas Eve (never, ever give presents on Christmas day).