For a 100% straight response..........
If she would be a non-biased judge, then have her measure him and then measure you, separately. A completely straight guy isn't always going to whip out a raging hard on in front of another guy. However, that may change after a number of drinks... That's how my best friend in HS got measured. He and a couple of others were at a party and he would always brag that he's big. One girl said to prove it and she got out a measuring tape. I think he was the only one measured, but from there on out, his brothers even bragged about it. This is my brother so-and-so... he's got a 7.5" dick. :biggrin1: