Sorry I can’t give you much to go on.
It’s maybe 5-10 years old. It’s about a bank robbery, with the robbers as the protagonists. They either have no guns, or fake guns. It’s probably a comedy, in the vein of Ocean’s Eleven or The Italian Job.
Is it American?
Any idea who’s in it?
Could you be thinking of this film?
Bandits
Any more of the plot? Was the target a bank, an armored car, a casino, a reclusive billionaire? Does the robbery succeed or not? Any plot twists, holes, doublecrosses, car chases, love interests? Drug usage, nudity, violence? How funny was it, for a caper movie–Martin Lawrence Funny, or Eddie Murphy Beverly Hills Cop Funny?
Male or female protagonists? Blonde, brunette, redhead? Black, white, Hong Kong?
Starring? A-list people, B-list people, direct-to-video people, porn-stars-branching-out people?
In English, French, Chinese? Dubbed or subtitles?
See, you know more than you think you do, Grasshopper. 
I will ask about Bandits.
I heard about this movie from someone who has a basic inability to remember any sorts of details about movies whatsoever.
I got the impression that it’s an American film, though.
It might be Airheads, which is about a loser metal band that takes a radio station hostage to force them to play their demo tape on the air. They use realistic looking squirtguns when they take the place over. Stars Brendan Fraser and Adam Sandler. Pretty funny, over all.
Bandits is pretty forgettable, FWIW.
How about Sneakers? They test bank’s security systems. Then the plot switches to involve a chip that decode anything that has been encrypted.
Was it the one with Bill Murray dressed as a clown?
Quick Change: Quick Change (1990) - IMDb
Definitely not that, as that was another movie we discussed in the same conversation.
Could it be the remake of The Ladykillers with Tom Hanks?
It sounds like Snatch – there is a bit with some bank robbers in it, as I recall.
“How come your gun says Replica and mine says Desert Eagle point five o?”
If the OP’s friend can’t give a better description than that of Snatch, I’d check for brain damage.
Sammy Jankis could remember Snatch.
The first movie that brings to my mind is Inside Man. It had Clive Owen and Willen Dafoe. Could that be it?
It’s called Inside Job. An IMDB search turns up a bunch of movies with that name, and none of the descriptions sound right.
I bet it is Inside Man.
Much older than that (1989, to be precise) but Disorganized Crime was the first film to come to mind. Far funnier than any film involving Corbin Bernsen ought to be.