Beware of flower scam in major cities. Don't take anything from strangers to avoid being charged.
Use public transport in Europe. Renting cars is unnecessary, and automatics may require special requests.
No laughing at Holocaust memorials. Photos discouraged. Nazi salute is illegal in Germany
Keep wallet in front. Carry essentials. Avoid fancy phone wallets.
Be aware of store hours in Europe. Don't expect them to be open late or on weekends.
Be polite, direct. Avoid small talk. Tipping not customary. Americans, tone it down.