A dinosaur sized douche-bag, a person worse than a douche-bag but not as bad as a fucktard.
Gina: Matt never texted me back last night.
Bob: What a douchesaurus.
A big jerk, idiot, imbecile. A rude person not willing to admit his or her mistake(s).
"Some guy came in the diner the other day and didn't leave me a tip; even after I gave him a free order of fries! What a douchesaurus!"