In scene 4, Blanche lays out her objections to Stanley: There's something downright bestial about him! . . . He acts like an animal, has an animal's habits! Eats like one, moves like one, talks like one! There's even something sub-human something not quite to the stage of humanity yet! Yes, something ape-like about him, like one of the pictures I've seen in anthropological studies! Thousands and thousands of years have passed him right by, and there he is Stanley Kowalski survivor of the Stone Age! Bearing the raw meat home from the kill in the jungle! . . . Maybe he'll strike you or maybe he'll grunt and kiss you! Remember that the opening scene—in which Stanley throws a packet of meat to Stella—occurs before Blanche comes on stage (so she can’t be referring to that moment) and then provide an explanation of the multiple ironies of this passage.

The ironic thing about this passage is that Blanche is, in some key ways, more like Stanley than she realizes. She complains that Stanley is motivated by brutal lust: being very blatant with his sexual desires. However, Blanche herself is driven by desires, particularly sexual ones. Remember that she's only living with her sister because she was fired from her teaching job for sleeping with a student.
Blanche did not need to see Stanley throw the meat pack to Stella, because she's already witnessed the way he talks, dresses, and eats. Stanley is not ashamed of his lack of social graces and airs. He takes pride in being "common." And the greatest irony of all is that Blanche is only listing what Stella finds most appealing about Stanley (e.g., his virility, his lack of manners, etc.). Stella did, after all, leave Belle Reve and she chose to live with a man who represents the total opposite of the refined world she came from. As Stanley later states, Stella loved being taken from those "columns."

In this passage, Blanche is largely objecting to Stanley's masculinity and physical aggression—which, together, establish a recurring theme in the play.
Aside from both possessing desire and carnal lust, as was mentioned by other educators, Blanche is not taking Stanley's constant drinking into consideration. She makes no mention of it, even though alcohol exaggerates his masculine tendencies and physicality. This is ironic, because Blanche is criticizing Stanley's behavior which is magnified by drunkenness, while she herself consumes copious amounts of alcohol.
Blanche readily accuses Stanley of inappropriate behavior while hiding important details of her past that would also be deemed inappropriate; for instance, how she had been kicked out of the motel she had been staying at for having multiple sexual encounters with men.
Blanche readily points out Stanley's flaws and is brutally honest about his behavior, wishing Stella to see her husband in a different light; this is ironic because Blanche lives in a fantasy world and actively attempts to escape her own reality.

Ever since she arrived to stay, Blanche has been a regular witness to Stanley's neanderthal behavior. He's a hulking great brute, physically and verbally abusive, always ready to pick a fight with anyone who crosses him. His crude manners appall Blanche, the delicate, refined Southern belle. The two are like chalk and cheese in every conceivable respect, and their mutual hostility and antagonism is there right from the start. Blanche didn't need to see Stanley throw a packet of meat to Stella to know what kind of a primitive throwback he is.
What's ironic in all of this is that Stanley's behavior, like Blanche's, stems from his various desires—to be lord and master in his own place, to be respected, to live up to society's expectations of how a man should behave. It's just that Stanley expresses those desires in a completely different way to the elegant, educated Blanche. Even more ironically, Blanche and Stanley share the most intense desire of all—to secure the sympathy of Stella, who's caught up in the middle of their epic battle of wills.
A further irony in Blanche's litany of complaints against Stanley's ape-like regression is that she's not saying anything that Stella doesn't already know. She seems to overlook the fact that Stella's strongly attracted to Stanley precisely because of his overpowering, thuggish masculinity. Blanche thinks that by telling Stella some home truths about Stanley she'll somehow manage to get her sister to see sense, to realize that she's too good for Stanley and quit this abusive relationship. However, she's sorely mistaken in her assumption; Stella's going nowhere. Despite everything, her bond with Stanley is strong and set to get even stronger with the imminent birth of their child. No amount of colorful insults that portray Stanley as an example of evolution in reverse is going to make the slightest bit of difference.