"随便" 的英文口语表达方式有几种，常用的有：
casually
carelessly
offhandedly
nonchalantly
haphazardly
without much thought
其中 "casually" 是最常用的表达方式，意思是不放在心上，不在意的。
例句：
He casually mentioned that he would be leaving the company next month. (他随口说了一句，下个月就要离开公司了。)
She carelessly left her phone on the train. (她漫不经心地把手机放在火车上了。)
He spoke offhandedly about his plans for the weekend. (他随口说了一下周末的计划。)
She nonchalantly brushed off his attempts to start a conversation. (她漫不经心地拒绝了他尝试聊天的做法。)
He haphazardly threw his clothes into his suitcase. (他随手往手提箱里扔衣服。)
She did it without much thought. (她没有多想就做了。)
这些词语都可以用来形容一种不在意或者漫不经心的态度或者行为。