I've been listening to soundtracks from spaghetti westerns all day.
Tonight, while that music was still playing, I stalked my teammates in Battlefield 3. As soon as a guy would get into position to camp the enemy or whatever, I'd fire a smoke grenade at 'em. They'd move but after a few shots I started getting yelled at

It's most fun with snipers because if you fire it behind them, it totally gives them away. If you fire it into them it blocks their stupid sniper view.
It's also really funny to fire it directly in front of small squads as they advance towards a building or across a street -- they run right into it, get blinded, and then immediately get lit up by the other guys who saw the smoke.
By the way, if you get a jeep going fast and bail out so it coasts into your teammate and kills them, it doesn't count as a teamkill. I like driving jeeps into helicopters as they're taking off too. Or bailing out over the ocean when I'm flying a full transport chopper.
It would be a lot more fun if there was ingame voice.