Victory sign with palm facing inward means "two" in Germany.

Tipping your index against your forehead means "crazy" and is considered a grave insult.

Making circular moves in the same situation means the same, but is much less common.

Thumbs up means either "one" or "good job", though the latter mostly ironically.

Raising your index in the direction of the other, arm and wrist slightly bended, is the strongest gesture of dominance you can do when talking to someone.