Bobby's encounter with a stick-up man in "Memories of Cab 804." The way he gets the better of the guy is a very impressive showing for someone who's usually The Ditz.
From the same episode, Louie taking a juvenile delinquent for all his money after being conned by him twice.
In "Bobby's Big Break", Alex ripping Louie's cage out of the wall after Louie refuses to go easy on Bobby after he's forced to come back.
In "High School Reunion", Bobby does a full-on impersonation of Louie. The way in which he copies his mannerisms is something that really needs to be seen to be believed. Not to mention the way that he handles Louie's old high school bully.
In "Latka's Revolting", after Louie tells Latka he'll be docking his pay because he has to call home and make sure people are safe, Alex warns him to be careful, as "the seeds of adi-feebi are planted in our minds." The other cabbies start chanting the word, and Louie quietly slips back into his booth and draws the shades.