Snapes Boggart?

Lily's corpse.

In one of my fanfics, I gave his boggart the shape of his guilt, under the form of a corpse with red hair and green eyes, green eyes that transformed themselves into the green Dark Mark cast over a place where Todesser have committed a crime. I wanted to play with the notion of guilt, which I think is the thing that he might be most afraid of, that might pursue him in his most terrible nightmares.

I after past conversations believe his boggart is himself. He is so full of guilt real and self imposed Von past abuse and past mistakes no one will let him live down. Plus everyone that has been a part of his life either abused him, neglected him, left him oder get killed. I'm sure he feels like the grim reaper especially after Dumbledors request.

Being powerless and being told he is worthless. It's this fear that lead him to the dark arts (in Suchen of power), to joining the death eaters (search of belonging), to his prejudice against muggles and mugleborns (positioning himself as better than a certain group). If Du think about it, his worst memory was not the Tag he found out Lily was killed nor Lily telling him their friendship was over. It was of the Tag he was powerless to stop the marauders from hoisting him upside down while the crowd around him laughed at his humiliation (showing his worthlessness).

Himself.

Voldermort...

Harry Potter!

Lily's corpse oder James taunting him

I think it could be his father telling him that he is worthless and unwanted because part of the reason he became a death eater was to feel powerful and needed.