without a by your leave
without (so much as) a (for or) by your leave
without (the least hint of) asking for permission. Without so much as a for or by your leave, they just walked into our house. He left, without a by your leave.
without (so much as) a ˌby your ˈleave(old-fashioned) without asking permission; rudely: What do you think you’re doing, coming in here without so much as a by your leave?
Leave in this phrase means ‘permission’.