I'm using the YouTube link (note: already taken down) OP provided in one of the comments to answer this question.
Basically, the lies that haven't come true according to this video are:
- (Conqueror's) Haki
- Having 8000 followers
- Medicine that cures all diseases
- Brave warrior of the sea
- King Usopp from hell
- Beating ten giant shadows
- Assisting in bringing down a bombman
- Descendant of Noland
- Being born on Sniper Island
Personally, I believe three of them have been verified in recent chapters though.
- Haki could be considered as truth as he indeed unlocked (Observation) Haki and he will most likely not discover Conqueror's Haki.
- Law's DF could be considered the medicine that cures all diseases as he could cure fatal diseases such as lead poisoning and could even cure the terminal illness called death.
- Assisting in bringing down a bombman is probably referring to the fact that he sniped Sugar the second time, bringing down the giant toys that were aiding.
For completeness, here are the lies that have been confirmed according to the same video:
- Pirates came to Syrup village (Black Cat Pirates)
- Saved a whale from North Blue (Laboon)
- Fought a huge goldfish with poop as large as islands (The goldfish at Little Garden killed by Brogy and Dorry. The same goldfish had pooped the island called Nanimonai)
- "Honestly, I know I'm a man among men, but you can't fall in love with me, girl. Not my fault if you get burned." (Basically what Sanji told the Okama)
- A big condor, flying through the skies (The big condors Chopper met during the time-skip. Usopp rode one during the reunion)
- Abominable snowman (Rock and Scotch, the Yeti Cool brothers)
- A beautiful female swordmaster who brought a lot of meat (Rebecca buying Luffy three bentos at the Colosseum)
- A huge mole inside the mansion (Miss Merry Christmas from Baroque Works)
- During the Syrup Village arc, they pretend to chase "Cerberus", while chasing a regular dog (Usopp met a real Cerberus at Thriller Bark)
- They also pretend to capture a dragon (The Straw Hat Pirates actually capture (eat) a dragon on Punk Hazard)
- Country of dwarves (Tontatta country)
- Legendary hero Usoland (God Usopp)