Within A Midsummer Night's Dream, Puck is characterized as a mischief maker. You can observe this characterization reflected both in the play's dialogue as well as in the actions he takes throughout the play. Insensitivity is certainly one of his prominent traits.

In his first appearance in act 2, scene 1, Puck is referred to in the following terms:

Are not you he
That frights the maidens of the villagery,
Skim milk, and sometimes labor in the quern,
And bootless make the breathless housewife churn,
And sometime make the drink to bear no barm,
Mislead night-wanderers, laughing at their harm?

To this, Puck gleefully replies in the affirmative, referring to himself as "that merry wanderer of the night."

This dialogue establishes Puck's primary characterization, but these words will be reinforced by his actions throughout the play. Thus, we can observe Puck turning Bottom's head into a donkey's, for example, or enchanting mortal men to fall in love. Indeed, note that when Oberon discovers that Puck had charmed Lysander, Oberon himself states,

This is thy negligence: still thou mistak'st,

Or else committ'st thy knaveries wilfully.

Here, Oberon's words raise the possibility that his servant might have enchanted the wrong target on purpose. The very fact that Oberon takes this possibility seriously establishes that this sort of malice would have been entirely within Puck's character.

Thus, we can see throughout the play an attitude of manipulative whimsicality where Puck (as well as Oberon) is concerned. He delights in causing chaos and gives little consideration to those impacted by said mischief.