The phenomena on Urban Dictionary of submitting a name, then writing a definition for a singular person painting them in a negative light.
If male, the definition will either claim the subject is homosexual, possesses a small penis, or is a "douchebag." If female, the definition will describe her as a "slut," a "bitch," or "fat."
A slightly intelligent Trash-Talker will try to disguise their entry with things like "he/she," or using the name in question as a title. This will (sadly) fool some editors.
Urban Dictionary Trash-Talking is widespread, with about 40% of entries reviewed being UDTT or UDA.
The converse is Urban Dictionary Arrogance.