Goomer Pyle was a character from the TV series known as "The Andy Griffin Show". In the show Goomer Pyle was a marine who wasn't the smartest person ever. Usually if someone is called Goomer Pyle they are being called: stupid. Basically you've just been insulted.
In the movie "Full Metal Jacket" one of the characters was called Private Goomer Pyle because he was a bit mentally challenged.