Surprisingly, in the UK it is illegal to do that to a king/queen.
http://press-pubs.uchicago.edu/founders/documents/a3_3_1-2s8...
From wiki: According to the law in force, it is treason felony to "compass, imagine, invent, devise, or intend"
http://press-pubs.uchicago.edu/founders/documents/a3_3_1-2s8...
From wiki: According to the law in force, it is treason felony to "compass, imagine, invent, devise, or intend"
It is doubly weird for the UK since the monarch is just a figure head. I wonder if the law applies to the prime minsiter (after watching London has Fallen, I guess not).