It's disrespectful and not allowed to wear revealing clothing (including shorts) in the Sistine Chapel and St. Peter's basilica.
--Vatimir
10
Don't be vocal about your dislike of the Catholic religion. Keep it to yourself.
--Vatimir
10
Do not try to ask for passport stamp at Postal office in St. Peter's square. They will not stamp passports. Don't even ask. They have signs saying it and will be rude to you.
--Vatimir
00
Be polite and courteous to the Swiss guards. Don't take their pictures. Don't treat them as if they're a zoo animal, even if they do wear a funny uninform.
--Vatimir
10
Latin is the official language, so feel free to use it with people, but don't expect them to know it. Some of the Vatican officials do speak it, though!
--Vatimir
