If you describe something or someone as forgettable, you mean that they do not have any qualities that make them special, unusual, or interesting.
例句
He has acted in three forgettable action films...他曾經在3部不起眼的動作片中出演角色。He was average height, average build, with mousy hair and a forgettable face.他中等身高、中等身材、灰褐色頭發，長著一張過目即忘的臉。