[jasontsui]

Hm - a lot of comments here seem to suggest that your prank ethics are sound- but I think a lot has changed in recent years. With the proliferation of Nathan for You, #goating, College Humor prank wars, youtube shows, etc - when weird things begin to happen, my reflexive response is almost immediately "This must be a prank." and to start accusing possible culprits in a spray and pray attempt to "figure out" the situation. If the pranker fessed up immediately, then there wouldnt be much of a prank.

With prankees increasingly guarded, maybe there should be some leeway in this rule.

[Uhhrrr]

Yes. In general I still don't think it's fair play to not admit when confronted, but the fact that the prankee was also a pranker, and ultimately said "well played" and characterized the earlier denial as "OP and gf played it cool" means that OP was just calibrated to the prankee's expectations.