Green’s Dictionary of Slang

1. one who lacks control of his emotions, because of excitement or fear.

1960		H. Pinter Caretaker Act III: They’d take one look at all this junk I got to sleep with they’d know you were a creamer [...] Nobody knows what you’re at.
1968		A. Buzo Norm and Ahmed (1973) 7: Ar come on, Ahmed, don’t give us that. Don’t be a creamer all your life. Tell me a bad point.

2. an outstanding example of something.

1954		‘Hot Rod Lexicon’ in Hepster’s Dict. 2: Creamer – Outstanding car.
1969		A. Buckeridge Trust Jennings (1989) 77: Cor! What a mess! That’s a right creamer, if ever I saw one.
2010		K. Richards Life 14: And when the trunk was opened that was the real creamer. It was legs-in-the-air laughter.

3. a general term of abuse.

1959		W. Hall Long and the Short and the Tall Act I: Wrap up, boy! Look. Don’t be a creamer all your life.
2005		P. Howard Curious Incident of the Dog in the Nightdress 4: He was the creamer I swapped houses with.