Hooray for the revival of a topic untouched for the last eleven years! Here's a few I uncovered in the editor.

Diamondus (JJ1): "Tim is a dork"

Lagunicus Boss Level (JJ1): "F*** off lamerz"

Marbelara (JJ1): One of the white marble blocks says "Nick" in small letters.

Deserto (JJ1): Three messages.

"Cliff is Co|" [Presumably Cliff is Cool]

"Eat Me"

"Epic Rules"

Deserto Secret Level (JJ1): A shadowy image depicting several people standing in a line.