Borderlands – “Hey! Over here!” challenge: where is the hidden claptrap located

Here is the list of places for "World Traveler". I did not include the other locations for the other 4 achievements as those would be included to get this achievement. Hope this helps.

Windshear Waste

• Claptrap's Place
• Frostbite Crevasse

Southern Shelf

• Liar's Berg
• Gateway Harbor
• Wreck of the Ice Sickle
• The Soaring Dragon
• Bandit Freighter

Southern Shelf Bay

• Ice Flows
• Ebonfloe
• Blackburn Cove

Southpaw Steam & Power

• None

The Dust

• Boot Hill
• Ellie's Garage
• Old Dahlwell Oasis
• Bug Gulch
• Moonshiner's Shack
• Goose's Roost
• Hodunk Speedway

Bloodshot Stronghold

• Rat's Nest
• Satan's Suckhole

Bloodshot Ramparts

• Shrine of the Gunbringer

Friendship Gulag

• None

End of the Line

• Snowblind Defile
• Terminus Plateau

The Fridge

• The Rat Maze
• Crystal Claw Pit
• Frigid Cleft
• The Rakk Cave
• Icemaw Grotto
• Stalker Hollow

Fink's Slaughterhouse

• Fink's Slaughter Factory

The Holy Spirits

• Ale Wee Cavern

Caustic Caverns

• Oozing Discharge
• Dahl Deep Core 06
• Rumbling Shore
• Nether Hive
• Varkid Ramparts
• Abandoned Mining Site
• Infested Warehouse
• Guardian Ruins

The Bunker

• None

Control Core Angel

• None

Marcus's Munitions Storeroom

• None

Ore Chasm

• None

Hero's Pass

• Guardian Slag Heap
• Emergency Supply Cache
• Drift Mouth Access

Vault of the Warrior

• None

Terramorphous Peak (Not Required)

When you get to Sanctuary, he gives you a quest where the reward is to access his stash. Once you complete it, you'll have a temporary option to hit a button (Q in the PC version) to give him a high five. He'll raise his hand.

At that point, hit your melee button (V in the PC version) to attack his hand. This will count as a high-five.

Be warned, though: if you're playing co-op and someone else completes the high-five, Claptrap doesn't allow you to request another one. :(

Edit, since this is the accepted answer: There is at least one other opportunity that has been identified by other answers on this question as times when Claptrap will ask for a high five. Here's the full list:

• After "Claptrap's Secret Stash" quest
• During the "Wildlife Preservation" quest

In all cases, the tactic is the same: When he holds up his hand, use your melee attack to hit it.

On a side note, once I'd given him the high five as part of "Wildlife Preservation", I could request one at any time. Even if you don't give Claptrap the high five in "Wildlife Preservation", as long as you complete the mission you can request the high five at any time. Aim at his hand and press V