He resembles a life-size vegetable.
Most of the humor in the show seems to come from Broccoli Head not being able to pronounce the names of the other characters, and ending up babbling instead.
Scooby-Doo! Mystery Incorporated
Later, Dr. Luis de Potrillo was chained on his sofa for thinking he was the creature. While they were waiting, Shaggy and Scooby watched Broccoli Head delivering a package to Potodebblepots which they laughed at.
The spookafied children surrounded Fred Jones, Jr., Daphne and Velma Dinkley, but Fred stepped on a TV remote showing Broccoli Head on a TV, captivating the spookafied children attention, and causing them to laugh. Que Horrifico was outraged and told them to attack, but the "Terrorbogattoes" only response was to take off their costumes. (The Song of Mystery)
"You wanted to see me sir".
"Yes Mr. Gloobafabie, Mr. Colthathen".
"Dabbledabbegabbleye... uh Dapflegne".
"Delivery from Hoslpenibbleyens."
"Delivery from Besl...ermelonbutl."