Dear Canker Sore,
Hello there. I've noticed that you moved into my lower lip about a week ago. I appreciate that you find me to be a hospitable host, and hope you've enjoyed yourself.
You are roughly the size of a pea. You hurt. Excessively. You don't seem to be getting better so much as you seem to be getting more comfortable. Normally, I'm able to ignore this sort of thing and let bygones be bygones until you go away, but you're making chewing hurt. You make licking my lips hurt, which is unfortunate, because when I have a cold, I lick my lips approximately three hundred times an hour, and I don't know if you've noticed, but I'm getting over a cold. So I could do without your aggravation. So if you wouldn't mind, I don't know, buggering off, that would be great.