I had never heard this expression before, although it gave me ideas when I read it in your question. I looked it up at http://www.yourdictionary.com/tin-god, which says, "A tin god is a bossy person who receives more respect than he or she should receive. An example of a tin god is a student who pushes everyone else around because the others are afraid of him."

"Playing little tin God in someone's life" is how I've heard it used. I took it to mean what the others have said, that is acting like you are important/ or telling someone how to live their life. I won't play little tin God in your english learning any longer :D

Well apparently it could also be referring to a song by an artist named, "Don Henley" who wrote a song called, "Little Tin God". It brings to my mind, cheap things which people buy as souvenirs. The song says people shouldn't pray to a little tin god. Tin, is a cheap metal, little god suggests a little statue to place on your shelves at home, or beside the table. If the saying existed before the song, I don't know but it refers to either the song, which says that figure is not of any worth, or the saying existed before the song and it is symbolic of a person who thinks too much of themselves. I personally favour the song because it sounds like it took someone's imagination to work it out, to coin the phrase, as people say. Little, tin and God all go together to make something which represents great importance but has great irony as it's rather worthless in itself. But that's a guess. http://www.lyricsfreak.com/d/don+henley/little+tin+god_20042060.html

Wow, I don't know :D That's a first :D Nice one DogLover