Aliens featured Bill Paxton as Hudson, the wisecracking PFC. In the extended edition, he even claims himself to be the "Ultimate Badass". That said, it's kind of understandable that he would freak out (Game over man! Game over!) the moment the aliens actually showed up, since they are pure horror. However, despite varying between making sarcastic comments and making scared sarcastic comments, he actually proves useful throughout the film, and his "Last Stand" certainly makes him CMOA worthy.
He underscores his nature in his introductory song, and first line, "Stand aside, I take large steps!"
"Brave" Sir Robin in Monty Python and the Holy Grail, who has a troupe of troubadours to follow him about and sing of his praises. Unfortunately he runs away at the first sign of danger, and they incorporate his cowardice into their song...
Britt, the titular hero of The Green Hornet movie is pretty close to this throughout the film, boasting about how awesome he is, taking credit for his partner Kato's achievements and generally being a barely competent blowhard. There's even one scene where a villain is about to hit them with a cement truck. Kato picks up a rock to shatter the truck's front window so Britt can shoot his gas gun at the driver, but all we see of Britt is him running away, firing his gas gun in all directions shouting "EVERY MAN FOR HIMSELF!!!!" By the end of the film, Britt does gain a measure of competence.
In The Wild Hunt, Bjorn is the big cheese of his Viking faction of LARPers and is always talking in Large Ham voice about being a warrior and going on adventures. When shit gets dangerous, however, he completely freezes. A girl lampshades it by screaming at him to justify all his talk and do something.
Spence in Ronin, played by Sean Bean, makes himself out to be just as much of a deadly Bad Ass as all the other operatives chasing after the MacGuffin. However, he is eventually exposed as a poser and told to get lost, which he does.
English Bob from Unforgiven. Hero of countless DimeNovels and known as the Duke of Death. However, in spite of his excellent gun skills, he has no stomach for stand-up fighting, preferring to attack drunk opponents from behind.
John Kreese in The Karate Kid. He makes himself out to be the ultimate warrior but is in reality a violent thug and a bully who enjoys picking on weak and defenseless people and uses dirty tactics to win. When he has to fight Mr Miyagi, he goes down almost without a fight and is shown for the coward he truly is. This is best exemplified in the second film when he starts beating up a student and Miyagi takes him down effortlessly and recites Kreese's earlier speech about mercy being for the weak, while Kreese is visibly scared.
Madmartigan from Willow is a subversion. He spends about half the film bragging about being "the greatest swordsman ever!" and the second half proving it.
Curiously, although this Trope is the Inverse of Cowardly Lion, the Trope Namer for that one fit this Trope when he first appeared in The Wizard of Oz, daring both the Scarecrow and Tin Man to fight him, saying he take them both at once (with one hand behind his back, standing on one leg, and with his eyes closed). He lost the attitude quickly.