6. The PDA is not accepted.

Reason: PDA is overly casual.
Exceptions include handholding and a pat on the back.
This precedent, established by Queen Elizabeth and Prince Philip, encourages individuals to keep their hands to themselves. Not only is it advised that the public keep their distance from the Royal Family, but the Royal Family themselves are forbidden from doing so.

People disapprove of PDA. ©Chris Jackson/Getty Images
Because they are expected to conduct themselves in a serious and professional manner when in public, royals rarely engage in PDA. They may clasp hands or give each other a quick pat on the back occasionally, but public kissing and snuggling are forbidden.