I want you guys to know, the word "fuck" appears in various forms across Harrow the Ninth 83 times, and across Nona the Ninth 151 times. (I also checked As Yet Unsent but there aren't any there there.)
Across all of that, M—/Mercy says it exactly twice. Once in a dubious by nature quote from John (not that I think he'd have any reason to lie there, but it could be paraphrasing/misremembering), with M— saying a few days before the escape ships launched:
John, there is no second wave. There is no third. They’re escaping. The trillionaires have converted everything to material resources. Half these passenger manifests are made up, these aren’t real people. They’ve fucked everyone, even the governments.
And then freaking out upon meeting Gideon in Harrow's body, one of the things she calls her is "you great big calf-eyed fuck-up!" (Also, fascinating choice of cow association there tbh??)
On the other hand, an incomplete list of other things Mercy has said:
everything about the Acid Jail speech obviously
"I will not help you make hyperpotamous travel happen, thank you for the option, my lord." / "That's quite annoying, thanks!" / quite a few others where she says thank you at the end of a complaint.
"and then she must have played silly buggers with—with the emission" (love her stammering too)
"It's a Resurrection Beast, honey!" (to G1deon)
"you wretched, cack-handed children" (Blood of Eden)
"Good luck!! Not!!!" (not the only "not!" either but TRIPLE exclamations, my beloved...)
"your nincompoop brother" (of Alfred)
"you vile, condescending son of a bitch" (Augustine)
"you mean-souled little man" (Augustine; what emphasis)
"that silly man-shaped worm" (to John of Augustine)
"you miserable ass" (Augustine)
"you abomination, you heresy, you failed ambition nineteen years too late" (Gideon)
"you dreary, repetitive leg" (G1deon)
A very few mild swears, and of course sometimes her insults are just like "idiot" and "infant", but there are so many that are so silly. If anyone can think of more, either creative insults or other silly or overly cute or overly polite stuff of any kind, please give them to me. I am collecting them. I must have them all. I love her so, SO much.