I do believe in it because I have / had close friends (including 1 aunt, and also my now-deceased father) that had this capability of cursing you with one look. This shit is real, and I don't care whether or not others believe it, I only hope they never get the chance to experience it because almost nobody knows how to defend against invisible spells that they don't even know exist, or believe they're real...
EDIT: maybe it's just a coincidence, but I believe that people with green eyes are the most prone to having this ability (both my aunt and father had green eyes, so I found this too big of a coincidence to dismiss the possibility of it being real, so if you know people with green eyes try not to get on their bad side