So at work I have to carry around a magnet with me for work related purposes. I normally keep it stuck to the metal joint on my lanyard.
A stroke of genius jumped into my head all the sudden today, and I walked up to two of my (male) coworkers to show them.
"Hey guys, check it out, my magnet sticks to the implants in my spine" *half twist, holds magnet to upper back, magnet sticks*
"Oh wtf"
"ugh"
"oh god"
"Do you think this is a good place to keep the key?" *magnet sticks to boob*
After I let them freak out for a while I pointed out that some bras have metal in them and they laughed.
I went and did the same thing to a gay friend at work and he kept going "ew ew ew oh my god that's gross" while turning around and walking away. When I pointed out it was my bra he said "Oh thank god, I was wondering how it was going through that much skin ... how am I supposed to know that anyway?"

(Titanium is used for implants, being that is non-ferrous and is not magnetic and cannot rust.)