When your friends use it: They are using this face to indicate "blow job" and not "wow"; either you posted a photo of a hot person, or they're like "blow me" because you posted something dumb.
When your aunt uses it: You used a swear word in a post and she doesn't approve.
When your crush uses it: If it's in reaction to a photo of yourself, it's a good sign. If it's in reaction to, say, a news article, your crush thinks you are dumb.
When your ex uses it: Block this person immediately.