I Think I'm going to cancel the dinner plans I had for my 18th birthday.
What's your reason for cancelling dinner plans?
I would just rather spend my birthday at home with my close friends instead.
I totally get that and more importantly, It's your birthday. Celebrate it how you want but make you tell the people you're canceling on ahead of time so they have enough time to make different plans. Not telling them or waiting too long would be extremely rude.
Well, I'm going to go eat out at my favorite restaurant.
Oh, so you are going to eat out after all? Well I hope you have a good birthday dinner!