Never a relative, but I’ve definitely stolen from a few straight friends! I totally use it to inhale their sent while jerking off. One of my buddies (the one who i jerked off with during the baseball game) used to actually just give me his undies to use for that express purpose! The first time I could not believe he was actually giving them to me, knowing what I was going to do. He wasn’t even weird about it. I asked him, “so you don’t mind if I go upstairs right not and jerk off with these?” He said, “ha, no. Go knock yourself out.” So, I did! When I came back down, we played Monopoly together like nothing just happened.
Another friend (the one I mentioned in the story in Costa Rica) caught me and didn’t even care. I actually had a pair of his boxers and one of his sweaty T-shirts in my bed. He saw them and just smiled. He came and sat on my face on the bed and grinded into me. He was pretty heteroflexible.