My preference would be "all OSI approved licenses; not any one in particular, but all of them at once" (and yes: this might legally conflict, but I think that would be a feature in this case, allowing for even more hilarious descriptions).
In other words, licenses don't make certain uses of works forbidden; they make them _permitted_. If you license it under both GPLv3 and BSD, and someone does something permitted under BSD but forbidden under GPLv3, the GPLv3 can't forbid the BSD license.
That said, the current wording (the 'union of the terms specified' by all OSI licenses) is not multiply licensing, but something far stranger...