From Bulbapedia, the community-driven Pokémon encyclopedia.
A trendy phrase is a special saying introduced in Ruby, Sapphire, and Emerald Versions, with altered usage in the Generation IV games Diamond, Pearl, and Platinum Versions. In Generation III, the player is able to create their own trendy phase by combining a set of two or more words on the phrase selection screen.
In Generation III, the trendy phrase is selected by the player by talking to a boy outside Dewford Hall in Dewford Town and using the easy chat system. Although it is a tiny island community, if someone says something "trendy" there, it quickly spreads throughout the rest of Hoenn. Dewford Town is famous for these fads. Trendy phrases are usually passed around in Dewford Hall, called "Everyone's information exchange!"
The trendy phrase in Ruby, Sapphire, and Emerald Versions affects the pattern of Feebas on Route 119. By changing the trendy phrase in Dewford Town, the six tiles where the Feebas are positioned will change.
In Generation IV, a trendy phrase is an additional phrase which can be used in the easy chat system. They appear in the "Tough Words" category. There are thirty-two different words programmed into the game, but only one may be obtained daily. They can be learned from an elderly man in the north-easternmost house in Snowpoint City in Diamond, Pearl, and Platinum, and from an elderly man on Route 16 in HeartGold and SoulSilver. Receiving a new trendy phrase will not alter any game mechanics. They typically refer to science, business and the arts.
List of Generation IV trendy phrases