Whenever i ask chicks to come to an outing such as the beach they always seem to say yes they're coming a few days before the planned outing, and then on the day before when i double check to see that they're coming they say "oh i got something on cant make it". How can i deal with this problem so that these chicks stop being flakey toward me? This hasnt happened once or twice this has happened to me many times and it pisses me off. What i usually say is "haha your missing out on fun" or " next time then" is that the right thing or should i do something else??

Thanks guys