If your friend is a guy, he will understand and should.
If your friend is a girl, then make up a reason like "last minute dinner with grandparents", or "had to take a friend to <location of your choice> on short notice and he/she doesn't have a ride>".
If your friend is a girl, then make up a reason like "last minute dinner with grandparents", or "had to take a friend to <location of your choice> on short notice and he/she doesn't have a ride>".