why do male cats somethimes attack people

In the Animal Kingdom, eye contact in the feline family is a threat.

My big 3 year old cat has become accustomed to eye contact and has no reaction whatsoever.

AND

Cats often jump people or things that, to the average human observer, do not necessarily deserve such an attack. Often they think they're playing. Cats have thicker skin than humans, and they don't realize how much their claws hurt. My cat has fairly regular periods of hyperactivity (signaled by dilating pupils) around sunrise and sunset, as well as occasionally around what she has determined is "bedtime" for the humans (around 10 pm). Hyper cats zoom around the house, chase anything that moves, and often jump their humans. It's normal cat behvaior, although you can send "this is inappropriate" signals to a cat by either saying "no" very sharply (you have to use the same word consistently, and you should never use the cat's name because it will confuse these admonitions with other times when you're just calling him) or by keeping a spray bottle on hand and hitting him with a quick squirt of water (this has to be done immediately, so the cat associates the punishment with the behavior).

What is a little bizarre is that the cat is singling you out. My cat does this to my sister, but only because they have a habit of playing more aggressively together than other members of the family do (we think she considers my sister almost like another cat). I can't give you a surefire answer, but here are some things to think about.