Triumph the Insult Comic Dog is a frequent guest on NBC's Conan O'Brien show, where it chats cheerfully with guests, then turns surly and delivers his catch phrase "... for me to poop on."
In the 15-page lawsuit filed in federal court, Pets.com says Triumph is a "rip-off" of its Sock Puppet mascot.
The company also claims that Triumph attempts "to harm the sock puppet's audience appeal" and that an "undesirable, unwholesome, and unsavory mental association" in the minds of consumers has been created between its perky puppet and Smigel's cranky comic pooch.
Pets.com also contends that Smigel has stated in a letter to the company that its sock puppet is actually based on Triumph and has threatened Pets.com with a lawsuit of his own for trademark infringement.
Neither Smigel nor Pets.com was immediately available for comment.