In the past I've had various fake boyfriends. Most notable was when I was 16, a 28 year old had taken to hanging round with my friendship group 😱 I saw him on a night out and he creeped right over to me. I grabbed a lad I knew, shrieked "this is my boyfriend say hi!" Then passionately snogged the lad until the creep creeped off creepily.
I was around before mobiles so when asked for my number I'd switch two digits round. That way I could cover it as a mistake if needed.