Does this negate the Laser Pistol power (as the Expendable Crewman has no Creeper attached)
-or-
Do we discard the Creeper (attached to a different Keeper) and the Expendable Crewman?
-or-
Do we discard the Expendable Crewman only?

See this question in a video!
Our Friend The Expendable Crewman, Part 1
Our Friend The Expendable Crewman, Part 2

A: The Expendable Crewman’s powers take precedence over the Laser Pistol’s. So even though you aimed and shot the Laser Pistol at the Keeper/Creeper combo, the Expendable Crewman leapt (tripped?) into the line of fire, and was offed instead, leaving the Keeper/Creeper combo still there to be dealt with some other way. Note that in Star Trek Fluxx, Ensign Smith functions as the Expendable Crewman, and in TNG Fluxx, Tasha Yar has that power.

So, knowing this, you might choose not to even point the Laser Pistol in that direction, knowing that annoying Expendable Crewman is hanging around – but that’s up to you.

(Keep in mind that if you’re the one with the Expendable Crewman, AND the Laser Pistol or Sword, you’re free to target your own Keeper-with-Creeper, without accidentally hitting your own Expendable Crewman. If the shot is coming from within his own ship, he will dutifully follow directions, and stand aside, letting the attack go through. It’s only when outside forces threaten that he gets flustered or over-brave.)