A lot of them owe a debt to the Military (TL;DR)
Some are carried over from dating and sex sites: (Again, TL;DR, but I'm glad that I was not the one to explain to a good friend and neighbor the acro “MILF”) (Mother I'd Like to Fuck)
But these are new to me:
TWANLOC = Those Who Are No Longer Our Countrymen, and
FYTW = Fuck You, That's Why
Some text is in white font, 'cause I suspect my dear Mother visits from time to time, just to see that the socks are picked up.