Normally, Crabbe and Goyle walked several steps behind Malfoy, Pansy walked to his left and Blaise floated somewhat ahead.
That was how they had walked through the school, and they kept that formation through the war.
The day of the Order's attack, the five had them were drunk, and so they stumbled 'round the camp, switching places and giggling.
When the curses came, Crabbe, Goyle, Pansy and Draco were hit and tumbled to the ground. Blaise thought they were doing marvelous impressions of rag dolls.
He was laughing as Order members carted him to Azkaban.
They say he's laughing still.