'Dobby had taken it upon himself to decorate the place for Christmas. 

He could tell the elf had done it, 

because nobody else would have strung a hundred golden baubles from the ceiling, 

each showing a picture of Harry's face and bearing the legend: 

HAVE A VERY HARRY CHRISTMAS! 

Harry had only just managed to get the last of them down before the door creaked open 

and Luna Lovegood entered' 

Harry Potter and the Order of the Phoenix 

Ch 21 The Eye of the Snake. 

Basically, Dobby is a legend.