As you know, yw means your welcome, which is a reply to 'ty'.
ywml is something old people say when they fail at chat speak, it means 'your welcome my love'
Jake: ty for the present, nan!
Nan: ywml : )
(i don't know why a nan would be on msn, but who cares?)
"You're with me, leather."
The now infamous pickup line used by Chris Berman to pick up a woman wearing leather pants in an Arizona bar.
"YWML is probably the worst thing to ever happen to Chris Berman."