chanpon
A type of pidgin or mixed language spoken by people who are native level fluent in both Japanese and English when speaking to each other. There is no formality to it, but is simply the mixing of both languages while speaking. The name is taken from the Japanese stew Chanpon.
I asked my Tokyo International School friend, "hey John, how have you been, genki? (feeling good?). We use chanpon when talking to each other.