Didn't people such as
@Pocket_Sand! and
@Gook Choy mention before that law enforcement have been out to see Lenny plenty of times already? Even so, there's probably not much they can do based on a screencap of a message that was acquired through a troll FB account.
If anything, Len would just point to the w-eens that fed him this stuff in the first place, so really all he's doing is talking shit over the internet which, like we do here, probably isn't anything major.
EDIT: Yeah, I definitely remember someone talking about how cops had been to Lenny's place a few times. All they can really do is warn him and tell him to turn off his computer for a while.