Unpleasant notes are inventory items in Problem Sleuth. They are the three detectives' main method of communication before they join forces.
Problem Sleuth and Ace Dick have sent a ridiculous number of notes to each other, ended by Ace Dick's "apology" note
reading "Problem Sleuth is OK sort of". Pickle Inspector has only written one, which is to Problem Sleuth. It informs Problem Sleuth just how impolite he is.
In the final stages of the battle with DMK, Problem Sleuth used a fully typed and notarized Unpleasant Note to cause a sudden spike in the boss's Sick Burn meter.
In Homestuck, Calliope receives
unpleasant notes from Caliborn via the Juju Modus they both use.
Problem Sleuth's unpleasant note to DMK.
Caliborn's unpleasant note to Calliope.