What should you respond if guy asks if you want to have a fling?

You should say "No!". The guy wanting to have the 'fling' is looking only for a one night stand just so he can avoid taking an ice cold shower, if you get my drift! No meaningful relationship come out of one night stands - in essence, you will be 'used' so that he can get his 'jollies' and possibly make you pregnant in the process. Doubtful he would stick around and offer support for the baby or for you. You should tell him that you are not just some temporary girl that he can just play with, and that you deserve to be treated better than someones door matt. Good Luck!