What’s the difference? It’s all about the delivery.
The eyebrows, the cigar, the leer – all Groucho. 
I once shot an elephant in my pajamas…
Hurray for Captain Spauling!
Happy Birthday Grouch!
From “A Night in Casablanca”
Enters club looking extremely disheveled
Woman: What happened to you?
Groucho: I was set up by a woman and knocked down by a car.
. . . . It’s all in the delivery, folks.
Actually, some of them might have been by Groucho. Unlike his brothers, Groucho hung out with the writers on all their movies. He became lifelong friends with many of them. He also participated in the endless rewrite sessions.
In addition, all the brothers were notorious for ad libs, and Groucho was known for his quick wit his entire life. When they performed on stage, they got bored and happily changed the dialogue pretty much at will. For the early MGM movies, they took them on the road and tested them with what we now call focus groups, letting the brothers try out all kinds of lines and keeping the funniest. Even when Louis B. Mayer put an end to this, they did a lot of experimenting on the set.
So there is at least a decent chance that some of these well known lines came from Groucho’s own twisted psyche. (I won’t argue with you about his offscreen persona.)
This might interest Groucho fans…
That’s an SD Classic Thread right there. 
“He may look like an idiot and talk like an idiot but don’t let that fool you. He really is an idiot.”
“Do you think I could buy back my introduction to you?”
“You’ve got the brain of a four-year-old boy, and I’ll bet he was glad to get rid of it.”
And something from one of my books:
“I must say that I find television very educational. The minute somebody turns it on, I go to the library and read a book.”
I have a nice little trilogy of paperbacks: Groucho and Me, The Groucho Letters, and Memoirs of a Mangy Lover. He was quite a good writer and some of his letters are to some of the best wits and writers of the mid-20th century. They’re all at Amazon and pretty good. The stuff with Steven Kanfer is pretty good too.
Fascinating man. Happy Birthday!
Please accept my resignation. I don’t care to belong to any club that will accept me as a member.
Who else remembers the Firesign Theater album: All Hail Marx & Lenin-with pictures of Groucho and John on the posters?
In 1989, the Republic of Abkhazia (in ‘the other’ Georgia) did the same thing with postage stamps of Marx and Lennon.