I was fooled

A lone knight is not sufficient material the only way K+N could win would be by a blunder into smother mate.  Where the king has no escape squares and the knight can land an uncontested check other than that K+N won't win

I think that K+N checkmate is possible if other side have at least one more piece.

There were pawns on the board... Pawns makes all the difference...

Not entirely true. The mate doesn't have to be smothered; the King can help guard squares along with the Knight. (A smothered mate is one in which the Knight gives check, and the enemy King is completely surrounded by his own pieces.) As covered in a different thread, one side having a King and Knight is not insufficient material unless the opponent has a bare King.

That's not entirely true either. In the following position, black has a knight and white has pieces yet black has insufficient material to mate:

E: oops

That's incorrect. The Knight and King are sufficient material to mate, in general, as long as the opponent has other material (your illustrated position notwithstanding). Whether any sequence of legal moves in a specific position can lead to mate (which, arguably, is insufficient material in that specific situation only) is a somewhat different matter. In the above position, Black has sufficient material to mate, but the position is disadvantageous, given White's material advantage and superior activity that hold Black at bay. The result of this game would be a draw by some other means (e.g. stalemate or threefold repetition).

1. ... Ng7 stalemate.

It's OK, my antibiotic buddy, don't stress it! At least you won't get fooled again.

What if black allows white to promote to nonsense pieces, and then mates him? Technically, white can still walk into checkmate there.

In Ebster's diagram, Black has no legal move that doesn't instantly end the game in stalemate.

...which is why sufficiency of material is a non-issue.

Why not 1. Ke7, allowing the pawn to promote?

Well it matters in similar positions in which it is white to move and she gets flagged. For example:

Oops. It's fixed now.

This is a unique position! Very nice. Interestingly, 1. Bxg7# is mate, but White ran out of time. Also, 1. B(anywhere else) or 1. Ke7 is stalemate, and so no sequence of legal moves can allow Black to win! This game is drawn, although I don't think I would call it insufficient material. That just seems wrong.

But as for the position in post #28, that is not insufficient material. If the Knight could only get to g6, Black would win. But 1. ... Ne5 (intending 2. ... Ng6#) is stalemate. So the draw is by stalemate, not insufficient material.

Wikipedia calls the rule "Impossibility of checkmate," and notes that this is usually due to insufficient material. So maybe semantically you are right, the material is sufficient even if mate is positionally impossible.

In post #28, white could immediately claim a draw due to impossibility of checkmate, or he could wait until black makes a move and the draw would be automatic due to stalemate.

That was the game Mr. Antibiotics played, won and... suddenly... lost...

After both knights have gone, 42.Kc3 Kxe5 43.Kxb3, there's plenty of pawns on the board for both sides... So, however black was at decisive advantage, its abandonment let white to win... I think now it's clear...

Rating points don't matter. You know you out-skilled him and he probably knows that too. I've met similar scumbags on Yahoo Chess.