Planned at 8pm, Received a 9pm text.

I just woke up. I'm so sorry. I feel really sick too. Please don't be mad.

double booked

"OMG i'm soooo sorry. I just realized I double booked a girls night out and dinner with you."

Phone problems...

A friend of mine actually used this excuse.

"I dropped my phone in some water and it broke for the weekend. Sorry I didn't call you to cancel. I forgot where dinner was suppose to be."

It was poorly executed but if done well, it can actually be believable.

distance

"OMG, that's so far! Can we do something closer?"

Rain Check

"Can we reschedule, something came up at work."