Has Snape's Worst Memory been explained by JKR?

[kvapost]

No: HPFGUIDX 180213

Does anyone know whether JKR explained why this particular memory was
Snape's worst? Before DH we had two versions: 1.being insulted in
front of Lily; and 2.calling Lily a mudblood.
Has JKR commented on that one at all? 
...If it was worst because of Lily, too bad for non-reading
movie-goers, as Lily wasn't even in the movie.