I will concede when the game could be won but the player wants to play a bunch of extra bs. This is especially true vs planeswalker decks when they could swing and win but instead want to + them all first. No dude I'm out. If I am especially in an annoyed mood I will quit if they play anything 1st main phase that isn't relevant to the dead on board turn.
Well in their defense it's always good to reach out to all your options so you have a bigger chance to play around a spell your opponent might have; especially if lethal is on board.
If it's relevant to that turn sure that's a good play. So haste creatures, sorcery buffs or sorcery direct damage that's fine I fault no one for that unless I'm tapped out or no cards in hand then you are still wasting my time.
1st main dead on board douche plays:
Creatures without haste and no ability that changes board state or buff.
Casting PWs with no ability to change the board that turn especially if it taps them out.
Using pw abilities that have no effect, like lilly last hope +1 with no opposing creatures or even worse using -2 gy recursion and cast a creature that has no effect on the turn.
Do nothing this turn enchants. Enchants that sac to remove a creature or always watching is excluded because they can change the board.
Playing instant card draw 1st main or life gain / life link especially instants on 1st main when they are way ahead. If I make a triksy play you can cast in response.
I could go on and on, so many plays that make me say "why would you do that?". All that annoys me highly and is a waste of time. I will hang in a game until the bitter end unless I feel like you are toying with me, it's insulting at that point.