The loudmouth is Wally Mail (Jack Lemmon) a braggard, a jester, an irritant.
While Wally is at a party. A news report on the latest killing from a stocking strangler has Wally ringing the police to claim he is the the man they want.
The other guests do not find it funny. Soon the police arrive and take Wally away for questioning.
They are not interested in Wally about the crank call. They think he is the killer.
A good performance from Jack Lemmon, who first thinks this is all a joke and then realises the seriousness of it all. By then it might be too late.
By that time the police has exposed him as a fantasist who exaggerates everything about him, making out to others that he is a big shot.
The story could had explored more if Wally was the killer, someone who might just be living a double life or that he was a convenient person to frame.