This is a trick that's sure to impress any date or job interview you happen to show up late for.
What I do is tell them that I've been followed.
This makes them curious, but I don't tell them anything. It's better to keep them curious, helps to build an air of mystery about you.
If you're meeting in a 7/11 check around the condiments at the hot dog stand to make sure there aren't any bugging devices. That way they know you're telling the truth. If you're at a job interview that your mother set up for you then just nod knowingly at whatever the interviewer says. Don't try to blame it on anyone or they might think you're crazy, just let them think that maybe there are things that you can't talk about. Often they'll start to think that maybe the same people that are following them are following you, which makes it good that you didn't tell them who was following you in case it wasn't the same group of people that was following them. Them thinking that you're being followed by the same people that are following them is good, because it gives you something in common and makes them more likely to give you a job.
And once you have the job, they'll be sure to understand when you're late that it was because you were being followed.