Other gamers always say "I beat Contra", or I can beat Double Dragon on 50 cents". In magazines like Nintendo Power, they'd say "finished", so I thought that sounded more professional for some reason. "I finished Ys Book II last night". So to this day I say "finished". I've even heard some people around the schoolyard say "solved". Which sounds alright for something like Adventures of Lolo, or Legend of Zelda, but sounds funny for "I solved Gradius III yesterday".
In Japan, when they finish an arcade game with one credit, they say "1 COIN CLEAR" , and I've seen guys on the Neo Geo forums say "I can 1CC Fatal Fury 2 on hard" I've never heard "clear" used outside of that, like "I can clear Castlevania without any powerups".
Most people here seem to "beat" games, what about you? Have you ever heard anything I didn't mention?