Choose a subject in front of a background with depth. Select your shortest focal length and take a close low viewpoint, below your subject. Find a natural point of focus and take the shot.
You’ll see that a very wide lens together with a close viewpoint creates extreme perspective distortion. Gently receding lines become extreme diagonals and rounded forms bulge towards the camera. Space appears to expand. The low viewpoint adds a sense of monumentality, making the subject seem larger than it is, and tilting the camera adds to the effect as vertical lines dramatically converge. Not the ideal combination for a portrait shot.
Both images were taken at 18mm, the angle of view appears to make the subject ‘larger than life’, it is an uncomfortable view and certainly not flattering. In the first image the buildings almost appear to be leaning in around the subject. In the second image the straight lines appear the bend slightly and the subject’s head seems smaller in relation to her body. This would be an interesting viewpoint for architecture maybe but not for portraits!