unfit coat/suit/shirt/pants; ill-fitting coat/suit/shirt/pants

coat:外套
suit:套装
shirt:衬衫
pants:裤子

不合身的衣服到底是上述的什么，要根据具体情况而定。

例：

I saw a weird looking guy soon after I got on the bus, who was sitting on the seat stilly with an unfit coat.
我上汽车不久就注意到一个外貌很怪的男人。他穿着一件不合身的上衣，一动不动地坐在位子上。

He sat in front of them, dressed in a plain, ill-fitting suit, never moving, his dusty face masking his age.
他穿着一件简单却不合身的外套，一动不动，从满是灰尘的脸孔上看不出他的年龄。