It’s 1967. Sandra Dee has just seated herself in the chair beside your desk. Being the douchecanoe you are, you adjust the angle of the mirror just a bit, and the reflection gives you what you wanted: an unobstructed view of Miss Dee’s grade-A legs.
This scene actually appears in the otherwise uneventful grade-B flick Doctor, You’ve Got to Be Kidding! And it had exactly the effect on this impressionable youth — I was 14 in 1967 — that you think it did.
But older and marginally wiser, I now feel compelled to warn you that This Could Happen To You:
There exists a crowdfunding effort to develop exactly this technology as an iPhone app, which as of the last time I looked had raised about eight times the original goal. The demand for this sort of thing by 14-year-olds of all ages is evidently substantial.