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...他曾经在3部不起眼的动作片中出演角色。He was average height, average build, with mousy hair and a forgettable face.他中等身高、中等身材、灰褐色头发,长着一张过目即忘的脸。