If this were play'd upon a stage now, I could condemn it as an improbable fiction

Wiki:

Robert Coates (1772–1848) was a British would-be-actor who became infamous for his mistaken belief in his own thespian prowess. His favourite part was Shakespeare's Romeo.

Robert Coates was born in Antigua in the West Indies as a son of a wealthy sugar planter. His lack of any skill in acting was obvious to his contemporaries. When he inherited the estate in 1807, he moved to Bath, England. He eventually drew the attention of the manager of the Theatre Royal, Bath and had begun to appear in plays in 1809.

Later he appeared in Romeo and Juliet in the part of Romeo - in a costume of his own design. The costume had a flowing cloak with sequins, red pantaloons, a large cravat and a plumed hat - not to mention dozens of diamonds - which was hardly suitable for the part. The audience cracked up with laughter.

Despite this apparent ridicule, Coates went on to tour the British Isles. If a theatre manager would hesitate to let him show his talents, he would bribe them. Managers, in turn, often called in the police in case things went seriously wrong.

Coates was convinced he was the best actor in business - or at least that is what he claimed. He forgot his lines all the time and invented new scenes and dialogue on the spot. He loved dramatic death scenes and would repeat them - or any other scenes he happened to take a fancy to - three to four times over.

Coates claimed that he wanted to improve the classics. At the end of his first appearance as Romeo he came back in with a crowbar and tried to pry open Capulet's tomb. In another of his antics he made the actress playing Juliet so embarrassed that she clung to a pillar and refused to leave the stage. Eventually no actress would agree to play the part with him.

The audience usually answered with angered catcalls and embarrassed jeering - and loads of laughter. His fellow actors would try to make him leave the stage. If Coates thought the audience was getting out of hand, he turned to them and answered in kind.

His fame spread and people would flock to see whether he really was as bad as they had heard. For some reason, Baron Ferdinand de Geramb became his foremost supporter. Even the Prince Regent (the future King George IV) would go to see him. In 1811, when he played the part of Lothario in The Fair Penitent in London's Haymarket Theatre, the theatre had to turn thousands of would-be spectators away. In another performance in Richmond, Surrey, several audience members had to be treated for excessive laughter.

Coates went on with his antics. Once, when he dropped a diamond buckle when he was going to exit the stage, he crawled around the stage looking for it.

Outside the stage Coates tried to amaze the public with his taste in clothing. He wore furs even in hot weather. He went out in a custom-built carriage with a heraldic device of a crowing cock and the motto While I live, I'll crow. In receptions he glittered from head to toe with diamond buttons and buckles. His predilection for diamonds of all kinds gave him the nickname "Diamond Coates".

After 1815 his performances decreased in frequency and his star eventually faded alongside his remaining fortune. He moved to Boulogne-sur-Mer, married and had two children, both of whom predeceased him. In old age he and his wife moved back to London.

Robert Coates died in London in 1848 in a street accident, when a Hansom cab hit him as he was leaving a performance at the Theatre Royal, Drury Lane. He was buried in Kensal Green Cemetery.