:: Try telling them the truth.
[[You]] sigh and get out of the car.  "Let me go first again," [[Billy]] says and he walks into the house and comes out about ten minutes later.  He motions to you and the two of you walk into his house and go to see his parents, Mr. and Mrs. Wegman.  

[[Mr. Wegman]] is sitting in an undershirt on a La-Z-Boy watching TV and [[Mrs. Wegman]] is sitting on the couch.  "So what's this nonsense about you turning into a girl?" Mr. Wegman demands.  <<if $Masc lte 60>>"I admit your face does look more like a girl's than it used to."<<endif>>

You tell him your (much abbreviated) story while he stares at you, his eyes never leaving you.  "Well, that all sounds like horseshit to me," he says.  "Billy says you've got tits now.  Let me see 'em."

[[Show him your tits.]]
[[Decline.|Don't Show Mr. Wegman]]