Actually it can be wrong like having fun with casual sex and ended up with aids.
Or smoking for fun until you develop a cancer.
Or having fun trying drugs and get addicted to it.
Or manipulating people then destroy other's life because, it's fun.
Reminds me of http://www.mangago.me/read-manga/akuma_chan_wa_momoiro/
I'm looking for this yaoi, there's the crazy couple like they do crazy shit to people, sometimes seduce other people into having sex with them or something, I can't really recall much but yeahh this is it