The Prince interpreted

[Dana]

No: HPFGUIDX 172751

Carol responds:
> We see that he and Lily are really friends, that he's different from
> the boys he runs around with (and blind to their faults). Oddly, as
> Valky also noticed, the worst memory comes *after* the so-called
> Prank, which means that James did not suddenly become noble and
> heroic. He's still willing to ambush Severus and publicly humiliate
> him. We're given no alternate version, so Severus's idea that James
> saved him because he got cold feet must be right.
<snip>

Dana:
I think you should read it again. (Sorry to lazy to quote) 

Snape tries to excuse Mulciber using Dark Magic on a girl and when he 
fails, he pulls in James Potter and his nightly activities. Snape 
already knew what Lupin was and not just from glimpsing him just that 
night. Lily specifically states that she knows his theories about 
Lupin, while she clearly had not talked to Snape after the ordeal 
happened. She goes on about Snape sneaking into the tunnel behind the 
Willow and that James saved him. Snape tries to make her see that 
James did not do it to be heroic but that he only wanted to safe his 
friends but never accuses him of trying to kill him. He just says 
that he doesn't want Lily to be fooled by him. 

Lily then goes on to say that Snape's friend's humor is just evil. 
Still Snape is not claiming that James and his friends tried to kill 
him for their amusement which would classify as evil. Lily was still 
his friend at this time and this would have been a good opportunity 
to discredit James but he doesn't. Lily knows something in the tunnel 
is dangerous or else she would not state that he was saved by James 
so Snape promising DD not to reveal Lupin's secret is not playing any 
part in why Snape would not use it against James. Snape does not even 
claim he was played a trick on and does not dispute he sneaked into 
the tunnel on his own accord. 

Snape lied to DD about why he was in the tunnel and tried to use it 
to get the Marauders expelled but his plan failed. And DD, 20 years 
after the fact, is still not buying. Lily writing Sirius a letter is 
also clearly evidence that she loved him on her own and not just 
condoned him as a friend of her husband and even though we have seen 
very little of Lily, I have to seriously doubt that she would except 
his friendship if he truly had set up Snape to meet his death.  

The scene actually says several things. Snape was not continuously 
bullied by the Marauders and the attack on Snape in SWM did not come 
totally out of the blue. Snape was as Sirius stated always sneaking 
around them, trying to find out what they where up to, trying to get 
them expelled. Snape was not always alone but hanging around with 
people Lily did not like and they indeed did things that made Snape 
unpopular by association. Lily states this when she says that people 
wonder why she is still even talking to him. 

Only JKR can resolve the issue of how Sirius played the trick on 
Snape but Snape did not go in unknowing. He took the bait in an 
attempt to get rid of the Marauders and in particularly James.  He 
tried to play it for all it was worth with DD and later Harry but did 
not dare to do that with Lily. 

JMHO

Dana