It has everything to do with the state of mind of every person at the table at the moment the intentional frog suicide is announced. If nobody cares, then it is not disruptive. This is probably the kind of group you come from (speculating). If it is disruptive to the majority of people at the table then it becomes a problem. This is the kind of group I come from.
See, I don't get this. At all. I *think* you are saying that the suicide frog is disruptive because it's so far out of the bounds of the expected that the only explanation for it happening is that another player is metagaming. (If I've got that wrong, please correct me.)
And yet...this is occurring in a world with floating castles, plane-shifting brain eaters, time stop magic, demon invasions, and rapiers. You, and the character you play, are totally willing to accept just about any crazy fiction. And yet somehow a suicidal frog is a bridge too far.
So let's approach this from another angle. Your characters enter dungeon room, and there on the floor is a large frog. Just as you are about to inspect this frog, the DM says that it leaps at your sword, and impales itself.
Is your immersion blown? Or do you assume there's some explanation for this that only the DM understands? I'm assuming the latter. (Again, if not, please correct me.)
So if we're still on the same page, what we have is this: when the DM introduces a suicidal frog it's fine, because crazy, bizarre things happen in this fantasy world, and this is pretty much the least of them. But when the player who is polymorphed into a frog does the suicidal thing, it's immersion-breaking metagaming because:
a) You know that according to the rules of the game the player can't introduce bizarre new magic on his own volition
b) You also know that according to the rules of the game this action would help him escape from a polymorph spell
See where I'm going with this? It becomes immersion-breaking for you because you are applying the "rules of the game" to the narrative scene. Your
character, ignorant of the difference between DM-actions and player-actions, would take this totally in stride. It's the
player who is bothered by it.
Thus it is metagame thinking that lets it be disruptive. A truly immersed player wouldn't notice.
My experience has been the opposite. Approaching it like a game first and a roleplaying experience second was pretty dominant when the red box came out. As time passed I’ve seen more and more care being put into the roleplaying side. Sometimes things went too far, to the point where players were being disruptive with their roleplaying at the expense of fun at the table. But more than ever before, I’m seeing a happy compromise that leans to neither extreme.
And I think that’s a really good place for D&D to be going in the future.
Are you staking out a position here that the kind of "metagaming" Iry and others don't like and "roleplaying" are opposites, and/or mutually exclusive? I know some people (@Saelorn for example) have a very, very narrow definition of roleplaying in which, they claim, using player knowledge is forbidden. But that's not the only, or even the most fun & interesting (imo) form of playing a role.