It generally maintains the tone you set. Remember that it outputs most likely tokens based on the system prompt of its owners + your system prompt + the whole conversation. If OpenAI and default system prompt tell it that it's a helpful cheerful secretary/assistant, you get best results if you talk to it "professionally".

I heard you could make Claude say "kurwa" a lot while helping you program in Go if you convince it that you want a conversation with your ziomek Seba from your backyard with whom you like to share kebab and browar, so there goes.