Here's my suggestions. (Sorry for a large post. Open to criticism.)
Items:
True Gentleman- Wear the Tuxedo Pants and Shirt, as well as a Top Hat
Fezs Are Cool- Wear the Doctor outfit with a Fez
It Belongs In A Museum- Wear the Archaeologist's outfit
The Achievement Is In Another Castle- Wear the Plumber outfit
HEY! LISTEN! HEY LISTEN!- Wear the Hero's outfit
Straight From Tortuga- Wear the Pirate outfit
Not A Wasp- Wear the Bee outfit
(More for other outfits)
Precioussssss- Wear a Diamond Ring
It's No Master Sword- Craft a Terra Blade
Biomes:
Welcome to Terraria- Visit a Forest Biome
Hypothermarama- Visit a Snow Biome
We Need To Go Deeper- Visit the Underground Layer
Dug Too Deep- Visit the Cavern Layer
Where's Hades?- Visit the Underworld
Evil Soil- Visit the Corruption
A Rotten Core- Visit the Underground Corruption
Blood and Gore- Visit the Crimson
What Even Is A Spleen?- Visit the Underground Crimson
100% Light and Fluffy- Visit the Hallow
A Rainbow Core- Visit the Underground Hallow
Columbia?- Visit a Floating Island
Sahara Desert Means Desert Desert- Visit a Desert Biome
Light Sources Make Good Meals- Visit a Underground Mushroom Biome
Weird Kind Of Farm- Create a Surface Mushroom Biome
'Welcome To The Jungle'- Visit the Jungle
'Sweet Child 'O' Mine' Was Better- Visit the Hardmode Jungle
*Loot Theme*- Visit the Dungeon
Easier Than Dark Souls- Visit the Hardmode Dungeon
THE BEES?- Visit a Beehive
I've Got A Bad Feeling About This- Visit the Lihzahrd Temple
What's On the Other Side?- Visit an Ocean
NPCs:
Khajit Has Wares to Sell, If You Have the Coin- Have a Merchant
A Good Healthcare Plan- Have a Nurse
Demolition Man- Have a Demolitionist
Sometimes, All You Need Is A Little More Gun- Have an Arms Dealer
Ready For Art Class- Have a Painter
Coat of Many Colours- Have a Dye Trader
Bad Omens- Have a Dryad
He Was Born A Ramblin' Man- Recieve a visit from the Travelling Merchant
Time For A Rave- Have a Party Girl
More Fish In the Sea- Have an Angler
Refugee- Have a Goblin Tinkerer
No More Broken Lights- Have a Mechanic
Potions and Rituals- Have a Witch Doctor
Don't I Know You?- Have a Clothier
You're a Wizard, Harry- Have a Wizard
Your Move, Punk- Have a Cyborg
It's Captain Jack Sparrow- Have a Pirate
He'll Grow On You- Have Truffle
#1 Contributor to Global Warming- Have a Steampunker
The Wrong Claus- Have Santa
Normal Bosses:
He Sees You!- Summon an Eye of Cthulhu
Dude, Now He's Blind!- Defeat an Eye of Cthulhu
Was That An Earthquake?- Summon The Eater of Worlds
Guess He Was Full- Defeat The Eater of Worlds
Using 100% Brainpower- Summon The Brain of Cthulhu
It Failed Your Test- Defeat The Brain of Cthulhu
Here Comes the Skeleton War- Summon Skeletron
BY THE POWER OF GRAYSKULL- Defeat Skeletron
Royally Gelatinous- Summon a King Slime
I'm the King Now.- Defeat a King Slime
NO, NOT THE BEES!- Summon a Queen Bee
ANYTHING BUT THE BEES!- Defeat a Queen Bee
Not for the Squeamish- Summon the Wall of Flesh
Dear God, What Have We Done- Defeat the Wall of Flesh and begin Hardmode
Hardmode Bosses:
All-Seeing, All-Deadly Duo- Summon The Twins
Death By Sibling Rivalry- Defeat The Twins
That Definitely Felt Like An Earthquake- Summon The Destroyer
At Least He Didn't Try Eating the World- Defeat The Destroyer
Skeletron 2: Electric Boogaloo- Summon Skeletron Prime
Four Arms Can't Touch This- Defeat Skeletron Prime
FEED ME SEYMOUR- Summon Plantera
Don't Feed the Plants- Defeat Plantera
That's Not Made of Clay- Summon Golem
Certainly Fought Like it Was- Defeat Golem
A WILD GYRADOS APPEARED- Summon Fishron
GYRADOS HAS FAINTED- Defeat Fishron
Micro-Biomes/Events:
Judgement, Eh?- Experience a Blood Moon
Far Out, Dude- Find a Meteor
Just Like Britain- Experience Rain
Does This Mean We're Heroes?- Experience a Solar Eclipse
Didn't Want to Go to Goblin Town- Summon the Goblin Army (it's a Hobbit reference)
Lvl 99 Goblinslayer- Defeat the Goblin Army
It's Snow Joke- Summon the Frost Legion
A Cold Response- Defeat the Frost Legion
They're After My Spices!- Summon the Pirate Invasion
Britannia Rules The Waves!- Defeat the Pirate Invasion
This is Halloween, This is Halloween- Summon the Pumpkin Moon
Beginning to Look A Lot Like Christmas- Summon the Frost Moon