The Battle of the Five Armies:
Dain’s “Oh, come on!” and “Good morning, how are we all?” and "faithless woodland sprite" lines
Every time Alfrid is on screen. (Only in this movie, not Desolation)
Anytime Thranduil smirks.
The cave troll with the battering ram on his head that bashes in Dale’s gates and falls over unconscious
Smaug’s undignified dying noises
"You call that a fair trade?" and Thorin's admonishing look (the whole scene between Bard and Thorin, actually)
"Except an army of elves, it would seem."
"If I'm not mistaken, this is the hafling that stole the keys to my dungeons from under the nose of my guards." "Yesss."
The Desolation of Smaug:
All the dwarves trying to cross the river at once in Mirkwood and Bilbo’s “Oh.”
Bombur jumping feet first into a new barrel in the river
Thorin’s clothes catching on fire and his immediate roll to his feet as if nothing had happened.
Gandalf introducing the dwarves to Beorn
An Unexpected Journey:
Bilbo passing out
Bilbo’s reaction to the dwarf home invasion. “I’m sorry.” “Apology accepted!” “Has it been canceled?” “What? No, nothing’s been canceled.” “That’s a relief!” And onwards. The whole beginning to this movie just cracks up.
Bombur catching the egg in his mouth (even funnier after watching the behind the scenes)
Every time Gandalf awkwardly avoids answering one of Thorin's questions
"If Baggins loses, we eats it whole." "Fair enough."
The Return of the King:
Hm, I’m sure I must laugh somewhere in this movie, but I can’t think of any moment off the top of my head.
The Two Towers:
“Shall I describe it to you, or would you like me to find you a box?”
Gollum’s scream that he does more than once
Gollum’s drama-queen reactions to having a rope around his neck
“They’re taking the hobbits to Isengard.”
The ent who ducks his burning head into the flood waters
The way Saruman silently pushes Grima and his torch back from his bomb
The Fellowship of the Ring:
“I like half of you half as well as I should like, and I like less than half of you half as well as you deserve.”
Merry’s “What was that?”
Elrond’s “Men are weak.”