"As far as you can tell" -- this is our stock answer to the question "How far can I (we) see?"
This started because when I would DM, I would frustrate the rogues in the group whenever they would try to detect a trap or disable a trap. I would make the roll behind the screen (percentile dice, since this started back in 1st ED) and say "As far as you can tell, there is no trap" or "As far as you can tell, you disabled the trap."
So when the PCs were mapping a dungeon, I would often use the phrase "as far as you can see" when describing long corridors, tunnels, etc. "It's a 10-foot wide corridor that stretches as far as you can see. There is a door 20 feet away on the south side and another door 25 feet away on the north side" etc.
One night in the middle of a pretty intense session in a complicated dungeon filled with traps, the rogue (actually a thief back then) was doing lots of checks. And I kept giving my stock answer. The person playing the thief was also the group's mapper. So at one point when they entered a new corridor, she asked, "How far does it go?" And out of habit I said, "As far as you can tell," rather than "As far as you can see."
It has become a running in-joke that has lasted 15 years.
"Bullet-proof pantihose" -- this usually gets uttered by someone any time the PCs go shopping for new items to improve their AC.
It started in a Cyberpunk2020 campaign in which one of the PCs, who always wore leather miniskirts, seemed to always get wounded in the leg during shootouts. Her legs were the only part of her body which had no armor. So she kept asking for bullet-proof pantihose.
Much to her surprise, one night I told her, "Yes, you can buy some pantihose made out of a lightweight kevlar-reinforced thread." I had bought a new equipment supplement that day that actually had armored pantihose and stockings in it. They didn't give much protection, but every little bit helped.
So now, even in D&D, when the PCs are searching for a way to improve their AC, someone will usually ask, "Can I buy some bullet-proof (or armored) pantihose?" Even the male dwarf asks this.
"War protester" -- This is the phrase used whenever a party member takes damage from friendly fire, including by his own hand.
This was inspired by the Vietnam War protesters in Asia who would set themselves on fire. One night the group's wizard cast a fireball spell in a room too small to contain the full blast. The backlash blew back into the hallway, frying the entire party. So someone asked the person playing the wizard if he was a war protester who wanted to set himself on fire.
We used to use critical hits and misses when playing D&D. A natural 1 was a critical miss, and carried a percentage chance for something bad to happen, such as a broken weapon or a blade stuck or damage to the wielder. So any time someone would roll a 1, followed by a DM roll that resulted in them inflicting damage upon themselves, someone else would say something like, "Are you one of those war protesters? Why don't you just set yourself on fire next time, it'd be a lot faster and more effective."
We also use it if someone gets hit during combat by a fellow party members, usually occurs when someone outside melee fires a missle weapon into the crowd or a poorly placed spell goes off with a party member inside the area of effect. The victim will ususally say something like, "Hey, watch it. I ain't no war protester."