What happens next?

How to ignore someone
Don't make eye contact.
Not making eye contact is the best way to ignore someone. Once you lock eyes, you're acknowledging that you know that person exists and are blowing your cover.
If that person is near you, avoid their eyes at all costs by making sure to make eye contact with every person but them, looking straight ahead, or even looking at the floor. If the person is shorter than you, then just stare right over their head.