Who knew that a few tree swings would get people so riled up? Well, duh, it's San Francisco. Over the past few seasons, fun-loving guerrillas at Unless Swings have hung old-fashioned, painted rope swings from the trees of at least three upwardly mobile neighborhoods. To date, nearly every one of those swing is now gone. They're gone from the Inner Sunset, gone from the Mission after inspiring a dramatic communitywide debate on the nature of fun (conclusion: It's not for everyone), and nearly gone from the Lower Haight, with just one on Waller Street remaining. So, before it's too late: Get out there, find that damn swing, and feel what it's like to fly through the air while other adults smile and wave at you.