Until recently, it was not a topic that I gave much thought to, since like most people raised in "mainstream" American culture, I considered it a foolish superstition, much like most aspects of folk magic. More recently, since I've been looking more closely at the underpinnings of folk magic, it occured to me that it didn't really matter what I thought about the topic, it's what the "recipient" of such a curse feels about them. So from that perspective, I've been trying to look a bit more closely things like the "evil eye" and petty curses.
It seems to me that such minor things ranging from an angry look in your eye, to a "withering gaze" and "The Look" fall into the spectrum of the "Evil Eye" (one is more generalized, while the other is specifically aimed). [n.b., if you don't know what I mean by "The Look", go into a library and start making noise -- watch the librarians. You'll see "The Look". My wife has one that I'm told can freeze your soul, although I've never noticed it myself...]
Essentially then, it would appear to consist of focusing your anger on someone, and perhaps wishing them ill (although in the latter case, there should be far more car accidents involving people who cut me off in traffic, so there may be more to it).
The Evil Eye might be construed as a form of basic psychic attack, intended to convey to the target just how pissed off you are and that you really want to carve out their still beating heart and feed it to them, but since you are restraining yourself, perhaps they could just drop dead instead.
Or from the opposite side, the Evil Eye, maybe cold chill of knowing that someone is angry with us, and wants to harm us -- the desire to avoid conflict that seems so prevalent with most people (heck, even as aggressive as I can be, I would prefer to avoid confrontation, barring other motivations).
There are any number of charms and talismans to block or protect one from the Evil Eye, one of the more common is the gesture known as the Manu Cornatu, or the "horned hand", while another is the gesture of the Fig. Since both of these are considered in some places to also be obscene gestures, it would not be too far off the mark to suggest that someone who "flips off" someone who is glaring at them, is simply (unconsciously) protecting themselves from the Evil Eye, by showing it means nothing to them.
The best protection, I suspect, from the Evil Eye, appears to be (based on observation
of people I see daily) the utterly selfish
obliviousness that wraps around most people in our mainstream culture. In most cases, though, a simple blessing should remove any effects from a curse passed simply by a gaze.
On the Other Hand, a decent set of psychic shields and a Fig amulet can't hurt...