In a play that meticulously strives to show both the good and bad in people, Yasha is pretty much all bad. He's so unlikable that we wonder if Chekhov was working out some sort of grudge. An opportunistic parasite, Yasha weasels his way into Lubov's favor; she seems to have a soft spot for less-than-upstanding men. Yasha's not in the house five minutes before he preys on Dunyasha:
DUNYASHA. When you went away I was only so high. [Showing with her hand] I'm Dunyasha, the daughter of Theodore Kozoyedov. You don't remember!
YASHA. Oh, you little cucumber!
[Looks round and embraces her. She screams and drops a saucer. YASHA goes out quickly.] (1.68-69)
She falls for him, though it's clear he's using her:
YASHA. [Yawns] Yes. I think this: if a girl loves anybody, then that means she's immoral…Somebody's coming. It's the mistress, and people with her. [DUNYASHA embraces him suddenly] Go to the house, as if you'd been bathing in the river; go by this path, or they'll meet you and will think I've been meeting you. I can't stand that sort of thing. (2.21)
He's happy to make out with her, call her cucumber (weird), and give her lessons on how to stay in her place. He's not so happy being seen with her or jeopardizing his job.
Yasha's also unhappy remembering that he has a mother. When he first arrives, he refuses to see her, and when he departs in Act 4, he complains, "She'll make me lose all patience!" (4.47). His mother is a reminder of his peasant past – the last thing he wants to think about. He can't wait to get on that train to Paris.
Have you noticed that he yawns all the time, too? He acts like he's just above it all, including Russia. After taking pains to point out the Lopakhin's champagne isn't the real stuff, he guzzles it:
YASHA. What's the use of crying? [Drinks champagne] In six days I'll be again in Paris. To-morrow we get into the express and off we go. I can hardly believe it. Vive la France! It doesn't suit me here, I can't live here ... it's no good. Well, I've seen the uncivilized world; I have had enough of it. [Drinks champagne] (4.49)
Yasha's unappealing character – his pretension, his dislike of work, his freeloading – seems to be a result of a new class structure in Russia sorting itself out. As Fiers says, before the Emancipation, "the peasants kept their distance from the masters and the masters kept their distance from the peasants, but now everything's all anyhow and you can't understand anything" (2.81).