Splosion Man

Unlock Coward's Way Out level skip:
Kill yourself a lot of times by using the Right Trigger to unlock this option.

Unlock Splosion Man Gamer Pic:
Beat single player levels 1-4.

Unlock Scientist Gamer Pic:
Beat multiplayer levels 1-4.

Unlock Premium theme:
Beat single player levels 3-18.

Unlock Hardcore Difficulty:
When you have beaten the game on Normal difficulty the Hardcore difficulty setting will become unlocked. To successfully complete Hardcore difficulty you must beat each level without dying and not taking any damage as doing so will result in instant death.

Unlock Dashboard Avatar T-shirt:
Break any glass to unlock the 'Splosion Man T-shirt.

Achievements:

A Little Help from Your Friends
Reward: 25 Points
Objective: Complete the Multiplayer game.

All Hail The Splode King
Reward: 25 Points
Objective: Complete the Single Player game in Hardcore mode.

Eventual Destruction of a Galaxy
Reward: 10 Points
Objective: Be on the lookout for an old friend.

Get Over Yourselves
Reward: 10 Points
Objective: Select "Credits" from the "Help & Options" menu and watch the whole thing.

Get Them Out of Our Schools
Reward: 10 Points
Objective: Eliminate 10 Scientists and stop them from spreading their filthy lies.

Lay Off the Caffeine
Reward: 10 Points
Objective: Splode 300 times in one stage.

Master of Controls
Reward: 10 Points
Objective: Attempt to edit your controls in the options menu.

Not a Portal Reference
Reward: 25 Points
Objective: Collect all 47 cakes in Single Player mode.

Omaha Steaks?, Delicious!
Reward: 15 Points
Objective: Create 5,000 filets.

Only Gandhi Would Be Proud
Reward: 10 Points
Objective: Finish a stage without killing any scientists.

Sugar High
Reward: 25 Points
Objective: Collect all 47 cakes in Multiplayer mode.

You're the Best Around!
Reward: 25 Points
Objective: Complete the Single Player game.