This is a straight forward guide to hopefully establish some solid rules for kicking players from parties for having poor HP values. I'll start by saying that I'm shooting for kicking the "really bad" ones, the ones who have dump stated con or demonstrate a complete lack of understanding the imortance of HP.
So first, using the lowest POSSIBLE HP a class can have. Everyone gets 20 HP at level 1, and every should get the 10 HP from Gianthold, these are "free" and easy to get. Beyond that you get your class die type per level, so the absolute minimum a player should have at 20 is:
Wizard, Sorceror = 110 HP
Artificer, Bard, Rogue = 150 HP
Cleric, Favored Soul, Monk, Ranger = 190 HP
Fighter, Paladin = 230 HP
Barbarian = 270 HP
So, if you see someone join your party and they have LESS HP then the class should have, feel free to kick them with impunity and stand in wonder and amazement at how they made it to 20 in the first place.
Assuming a player didnt' "Dump Stat" con, you can expect higher values as every 2 points in con above 10 equals 20 more HP at 20.
12 Con = +20
14 Con = +40
16 Con = +60
18 Con = +80
20 Con = +100
So on and so forth.
Its not unreasonable to expect that a player, even with a 10 starting con, can manage to get that con to 16. So using 16 as the "target" for easily obtainable con, everyone should have a minimum of:
Wizard, Sorceror = 170 HP
Artificer, Bard, Rogue = 210 HP
Cleric, Favored Soul, Monk, Ranger = 240 HP
Fighter, Paladin = 290 HP
Barbarian = 330 HP
Again, feel free to kick anyone with a level 20 toon with less HP then listed above. Though these players are better off then the previous list, at least these players made "some" attempt at getting HP. You might want to keep them for at least trying I guess.
Values over the above amount should be considered "OK" because not everyone has the "optimal" gear sets to push their HP's into the awesome range, and not every class has free feats to toss into taking Toughness 5x. However, feel free to belittle them and link all the awesome gear you have that you think they should have and then kick them from the raid that drops said gear, becuase they should have it already... you do.
(humor, recognize it)