SEIF 5
Two people are drinking together, one of them turns to his friend and says let's make Kiddush. The friend agrees. The Rambam says it is prohibited to drink (or eat) at that point until they make Kiddush. The Taz says that this is not equivalent to someone suggesting Bentching at the end of a meal. In that case, they may continue to eat without Bentching as long as they make another Bracha.