He was referring to Simon, or perhaps merely how horrifically Simon managed to put his foot in his mouth when talking with Kaylee.
Wash and Zoe come in right after this conversation between Simon and Kaylee:
Ah... Well, you're a, a kind of a genius when it
comes to machines... you always say
what you mean, and your eyes are...
Yeah? Eyes, yeah?
And, um... I don't know how to, um...
Plus, every other girl I know is
either married, professional, or
closely related to me, so you're
more or less, you are literally the only girl
in the world.
Those famous eyes of her darken considerably. She draws back.
Mm. That's a hell of a thing to say.
I was joking...
No, no, I get it. I do. Back on Osiris you
probably had nurses and debutantes
crawling all over you. But down here
at the bottom of the barrel, it's
No, that's, that's, that's not even --
Well, I'm glad I rated higher than
dead bessie here. < Why don't you tell
the cow about its beautiful eyes? >
[Nee GAO-soo NA niou, TA yo shwong
She is storming out just as Wash and Zoe are coming in. Simon watches Kaylee despairingly.
Oh my god, he's grotesque! Oh, and
there's something in a jar.
Immediately after, Zoe comments that he (Simon) scared her (Kaylee) away again, and asks if there is anyone he is good at talking to, so it seems likely that Wash and Zoe overheard at least part of the conversation.