'Shark Tank's' Scrub Daddy Sues, Says You're Sponging Off Our Custome

The company behind Scrub Daddy -- the most successful product ever pitched on "Shark Tank" -- is accusing a man of tricking customers with a knockoff sponge.

Scrub Daddy says Brian Reaux's attempt to push "Scrub 'N EZ" will confuse faithful Scrub Daddy customers because of the similar name and use of a smiley face ... this according to the lawsuit, obtained by TMZ.

In the docs, Scrub Daddy also has beef with Reaux marketing his sponge holder as fitting "perfectly in Scrub Daddy [sponges]."

SD has reportedly generated more than $75 mil since striking a deal with Lori Greiner on the show. The company wants "Scrub 'N EZ" to change its name, and quit using Scrub Daddy in advertising.