Neutral is defined by the socket (or not)
Each plug or socket has a design specification. That decides where neutral goes. For some socket types, it does specify at all.
Keep in mind that the very concept of neutral is not at all a given. Consider NEMA 6: no neutral, it's not in the connector.
Consider 480V "delta" (non-wild-leg), it is an isolated service which inherently has no neutral. It can be provisioned as an isolated system with no bias to ground.
Neutral Is Not Ground
Neutral and ground are bonded at the main service. That does not mean neutral and ground are the same. Neutral is the current return. Ground is a safety shield. It protects humans from shock, and equipment from lightning and ESD damage.
The Electrical Codes define neutral as a conductor, which means working current normally flows over it. Ground is not a conductor, and is not counted where conductors are considered, such as wire heating and eddy current effects. Current never travels on ground except during a fault condition.
What defines neutral is that it's near ground potential. It is not at ground potential because of voltage drop in conductors. Remember, while voltage drop in a "hot" conductor makes it drop -- voltage drop in a neutral makes it rise. It should still be within a few volts of ground.
Stick your knife anywhere you like - at your peril
If you stick your knife in the neutral pin, provided the system is healthy, you are OK unless you are also touching something at "hot" potential. However if your system has a problem, that may not be so. Electricity follows all possible paths back to source, in proportion to their conductance (inverse of resistance). If you have a damaged neutral or a broken grounding system, its conductance may be low enough that you look like a usable path. In which case you will be shocked.
The goal of neutral (and ground) is to give a much better path than you.