Is flirting with death a sin?

Most certainly it is a sin. Your life is not yours to do as you will for it belongs to God. He gave it and He can certainly take it away and it is not up to you to assist Him. This only applies, however, if you are a Christian. If you are sane (or another flavor of insane given the content of the question) then it's your body, go have fun with it, in whatever way you define fun.