(verb) To create hostility in others, causing them to attack you. This is frequently seen in MMOG's (massively-multiplayer online games) when a player draws the attention of one or more hostile NPC's (non-player characters) and is attacked by them. Also seen is the "chain agro", where the hostile NPC who was agroed causes the next nearest NPC to also agro on the player, setting up a chain reaction.

"Stay against the left wall to avoid agroing the goblins." "Look at that idiot, he just ran ahead and agroed the whole room."

to be angry or hostile for no reason

"that pitbull is fuckin' agro"

Undeserved hostility, one who expresses it, the act of it, etc. Seen in MMORPGs by players to complain about being attacked by a monster without them attacking it first. Can be a noun, verb, adjective, possibly adverb.

"Someone kill this agro!"
"OMG WTF DIS ZOMBY IS LYKE AGROING ME"
"Someone kill this agro zombie!"
"This zombie is attacking me agro"

To be/become agressive/angry/out of control.

"That gummer's comlpetely agro!"

The name of Wander's--the main character--horse in Shadow of the Colossus, significant if only because the AI engine that dictates his behavior is, by far, one of the most complex and realistic animal behavior engines to date. The horse is not without its eccentrics, however, and is prone to rather confusing responses when you issue him commands.

On foot, it will take forever to reach this Colossus. Riding Agro might reduce that time by half if I can ever get him to come over here!

Misspelled. See aggro.

People can't spell "aggro" right.

To aggrivate or antagonize someone, be it intentional or otherwise.

I agroed Hayley when I treid going backdoor on her without doing any prep work