You shouldn't even joke about talaq. some shaikhs say even joking counts as a divorce because talaq is a serious thing.

and you can't say talaq in one go. the man has to wait 3 menstrual cycles until the divorce can be finalized (this waiting period is called iddah). during that time the divorce can called off. but after the 3rd period there is no going back. and they are not allowed to remarry.

also if the couple wind up having relations during the waiting period of 3 periods they have to start the 3 months again.