Zig Zagged: New guy on the bomb squad, Bob, walks coolly away from an explosion... but then you see that this is a simulated explosion for a drill, and old hand Alex chides him for not following proper procedure... but then when the two of them are escaping a real bomb, Alex starts walking away because, damnit, it's too much fun not to, regulations be damned... but then as the two of them are walking side by side the blast wave picks them up and drops them on their asses, to the amusement of all.
Averted: Alex gets out of the building with time to spare. There's no chance of anyone walking or running away from this explosion.
Enforced: "And then Alex runs out of the exploding building." "I dunno, we could make it cooler and establish Alex as an explosives expert by having him look calm and walk out instead."
Lampshaded: "Hey, drama queen! Stop trying to look cool and take cover, idiot!"
Invoked: Alex is a bit of a ham, and sets some explosives just so he can make a badass entrance.
Exploited: Alex knows security or news cameras are rolling, and he wants to cultivate a badass impression on the police/public.
Discussed: "Don't worry, any second now he's going to casually stroll out of the collapsing building. Just you wait. *BOOM* ...Aaaaany second...Oh, Crap.
Conversed: "So, you think people can really just casually walk away from an explosion?" "Let's send it to Mythbusters!"
Deconstructed: In a cynical world, walking slowly away from an explosion gets you killed by shrapnel, which is not normally depicted in this trope or in Hollywood explosions in general. Also, if Alex really is the terrorist who planted the bomb then not blending in with the crowd when the bomb goes off is a good way to get noticed.
Reconstructed: All of that is true, but Alex isn't concerned about getting killed by his own bomb or getting caught; he's a terrorist, remember?