First, press D to reset the foreground and background colors to black and white. Then, select the
tool and paint in the layer mask over the subject. This can be a person, foreground object, or anything that you want to apply the Smart Sharpen filter effect to. If you want to erase any areas, use the
tool. Try to be precise with the painting because any inaccuracies will be visible later when we reuse the layer mask for another adjustment layer.

Hold the Ctrl key and click on the layer mask thumbnail in the Layers palette. This should create a selection based on the layer mask.

With the selection activated, click on the
button and choose Brightness/Contrast. This will create a new Brightness/Contrast adjustment layer and apply the selection to the layer mask.

In the Brightness/Contrast settings, set the Brightness to -50 then click OK.
Here's the final results of this photo effect. If you didn't do a good job painting the layer mask earlier, you can use the
or
tools to refine the layer mask.

Before and after:

100% crop:
