Dictionary / Vocabulary / タメ口
タメぐち · also ためぐち
casual speech; peer language; informal language
Also written ため口
タメ口でいいよ。
Casual speech is fine.
こんな喋り方が好きじゃないなら、タメ口でいいよ。
Unless you prefer talking like this, you can speak to me casually.