I came to this question after I saw a Facebook post about someone who passed away with everyone posting rip as a comment. Wikipedia tells me the following about the abbreviation of RIP:
"Rest in peace" (Latin: Requiescat in pace) is a short epitaph or
idiomatic expression wishing eternal rest and peace to someone who has
died. The expression typically appears on headstones, often
abbreviated as "RIP".
Possibly it is just me, but is it really appropriate to write RIP to express grief? It seems not decent to use an abbreviation in this case—is there not enough time to write it at least out?
Granted, after all the three letters do not root from modern age and internet like LOL, but have a historic background, plus it eases international verbal communication as it is with the word OK.