I may happend that you, like me, come across abbreviations when reading tweets that I have no idea of what they mean. I have collected the ones I see the most and that I either knew from before, or managed to figure out the meaning of, here. Feel free to add more in the comments!

Abbreviation Full meaning
AFAICR As Far As I Can Remember
AFAICT As Far As I Can Tell
AFAIK As Far As I Know
AKA Also Known As
DYK Did (Do) You Know
FWIW For What It’s Worth
ICYMI In Case You Missed It
IIRC If I Recall Correctly
IJK I’m just kidding
IMHO In My Humble Opinion
IMO In My Opinion
LOL Laughing Out Loud
OH OverHeard
OTOH On the Top Of my Head
POC Person Of Color
PSA Public Service Announcement
ROFL Rolling On the Floor laughing
TFW That Feeling When
TIA Thanks In Advance
URM UnderRepresented Minority
YOLO You Only Live Once

See also this appropriate cartoon I found on Twitter: