How old are you? Some people make more of an impression than others. There is so much biology and psychology that drives our urges. Thinking about someone doesn’t mean sexual attraction. The problem is, today the media brainwashes us into believing that we should act on every urge and to sexually explore. Since society not only removes the guilt, but encourages sin, we are truly in dire times.
The mind will focus on one thing at a time. It will also gravitate towards excitement and entertainment. If you really don’t want to think about this person then pick something else exciting to focus on. If you are concerned about being attracted to this individual then don’t masterbate while thinking about them. The chemicals released will pretty much cause a sexual addiction to those thoughts. Maybe not the advice you want, but good advice regardless.