Nexus offers a number of emotions(also called emotes) for players to use to express themselves. To have your character do an emotion simply press : (that is shift+;) and then a letter (from letters a-p).
Here is a listing of each emotion you can do:
:A Laughter
:B Grief
:C Shame
:D Affection
:E Boredom
:F Sleepiness
:G Suprise
:H Anger
:I Sarcasm
:J Shrug
:K Annoyed
:L Dance
:M Bow
:N Triumph
:O Downcast
:P Kiss
Side note: When you read a board or mail, your character automatically does the :E Boredom emote. Also when you are idle for an amount of time, your character automatically does the :F Sleepiness emote.