A real long shot but perhaps your friend is remembering the ending of PHENOMENA (85) (AKA CREEPERS). http://www.imdb.com/title/tt0087909/?ref_=nv_sr_2
Here's why it might fit (SPOILERS follow for those who've never seen it):
one of the film's "killers" is revealed to be a boy with severe facial birth defects. He attacks the heroine with a harpoon/boat hook. Maybe your friend conflated it all together with various other things. Happens a lot.