try-hard has many meanings
In gaming subculture slang, its common use is to describe a person that takes an intentionally fun or pleasant experience and tries to score/be the best in it at the cost of the enjoyment of others, and sometimes even his own.
not exactly a "bad sport"
Should be applicable on any situation where no one in particular is trying to be a big achiever because it clearly isn't the main goal, but one person decides he will do everything at his disposal to make his victory happen.
For example George participates at a couple's video making contest at his workplace for the funniest video.
where as everybody has got the same shot at the challenge, George hires 2 directors,a comedian, and pays all the employees in the bushiness 50$ to persuade them to accept having him as their partner.
edit: George deliberately breaks the "code of honor" for his own ego