I prefer not to step on toes so strongly, so I would be diplomatic and say something along the lines of "I did not anticipate dinner taking so long, so I cannot

I prefer not to step on toes so strongly, so I would be diplomatic and say something along the lines of "I did not anticipate dinner taking so long, so I cannot stay." Variations include "I am on a tight schedule. I'm sorry but 20 minutes in without even ordering is too much." If texting, I have found word choice to be crucial in delivering how upset you are since there is no tone of voice. Inclusion of an actual reason and/or "maybe next time" is completely optional.