informally
As children we used to address each other informally.
— Il gattopardo (1963)
Would you like us to use the informal form with each other?
— Fuck you, prof! (2013)
Ma non mi sembra che ci davamo del tu!
But it doesn't seem to me that we were on first name terms!
— Mosca non crede alle lacrime (1980)
Non sono abituata a dare del tu.
I'm not used to being on first name terms.
— L'infanzia di Ivan (1962)