[HPforGrownups] Has Snape's Worst Memory been explained by JKR?

[Bart Lidofsky]

No: HPFGUIDX 180256

kvapost wrote:
> 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.
Bart:
I think it was kind of obvious that this was the incident (albeit a 
final straw) that destroyed his friendship with Lily, which was, after 
all, his only real friendship (the Slytherin friendships were more like 
alliances than friendships; "you do for me and I'll do for you" types). 
Most people have, based on pressures, given in to an impulse to do or 
say something which screw up things, at least temporarily. Snape, in a 
moment of anger, destroyed something he had spent half his life 
building. That qualifies it for "worst memory", don't you think?

Bart