Just don’t ‘magically’ steal anyone’s underwear while they are out and replace it with something they wouldn’t normally wear.
That’s evil, and could be misconstrued.
And making their friend hold the evidence while also out is also evil.
Awww, now you’re taking the fun out of it! Okay, we’ll do it your way....while I slowly and discreetly pull you into the dark side. *evil grin*