I was watching one of USA Network's daily NCIS marathons and they run the episode where DiNozzo opens an envelope that has some sort of plague virus in it, and nearly dies before the rest of the team can find the person responsible and get an appropriate anti-viral.
What I noticed was how he opened the envelope. Rather than lifting the flap, or tearing open the top, Tony cut it open along a side, pinched the ends so the envelope pooched out, then blew into it, causing the plague-infected dust stuff to fly into the air and infect him. Whoops.
A similar thing happened to B.J. Hunnicut in an episode of M*A*S*H*, except all he got was a face full of what I guess was talcum powder (as he was the victim of a prankster, not a desperate lunatic). He opened the envelope the same way, and blew into it the same way, and had the same result.
In real life, I've never seen a person open an envelope that way. I've seen people carefully pry the flap loose, or cut along the top with a letter opener, or my usual tactic of wedging my finger under the flap and tearing it open. Cutting along the side, and blowing into it? Never. Is this something that used to be a common practice, and people stopped?
I have to assume someone was doing it, or else why would scriptwriters have characters use that method. Maybe it's a regional thing. Hunnicut was a Californian, I don't know where DiNozzo's from, though I know he was a Baltimore cop, so maybe it's a coastal thing. Or maybe it was a practice that died out because of the potential for prankery.