Grumpy Sims will autonomously "Shoo Off" cats sitting on top of furniture, even if the cat is asleep.
Grumpy Sims will grumble while waiting for their turn when playing Hopscotch instead of cheering the player in turn like the rest of the non-Grumpy sims.
Grumpy Sims can be "Mock (over their Grumpiness)" by another Sim, which greatly decreases relationship between the two Sims.
They share this attribute with hot-headed and mean spirited Sims.
Grumpy Sims will not react well to being splashed in a pool, and will furiously splash back at the offending Sim, decreasing the offending Sim's fun gain.
Sims with the Grumpy trait may develop the " Out of Sorts" moodlet upon awakening, making them potentially angry.
Grumpy Witch Sims will sometime autonomously cast malevolent spells and curses to another sims, greater chance while having the " Out of Sorts" moodlet.
This will grant them the positive "Let off Steam" moodlet if the interaction is accepted.
Grumpy Sims will autonomously use the "Complain About." type interactions.
Grumpy Sims may scream out in fury if something bad happens to a nearby Sim or if something bad happens to themselves.
Grumpy Sims are prone to autonomously arguing with other Sims, but rarely escalate to insults or fights as hot-headed, mean spirited or inappropriate Sims will tend to do.
Provides a bonus to Sims writing in the satire genre.
Grumpy Sims may react bored to certain interactions like the "Woo!" interaction from party animals or the "Tell Funny Story" interaction.
Grumpy Sims don't like to enthuse about something, they also don't like giving away compliments unless they have the charismatic, easily impressed or schmoozer traits.
This will result in a positive moodlet if the trolling succeeds.
Grumpy Sims have the option to "Troll on Forums" while on the computer.
To be specific, they take an innate and invisible -15 mood penalty.
It's more difficult to get the Sim into a good mood.
Grumpy Sims will usually get sad before getting angry or uncomfortable.