No quiero sonar maleducada, pero ese camarero fue bastante maleducado con nosotras.

Because the adjective changes to match the person it describes.

• maleducada refers to the speaker, who is female
• maleducado refers to ese camarero, which is masculine singular

So the sentence suggests:

• a female speaker: No quiero sonar maleducada...
• talking about a male waiter: ...ese camarero fue bastante maleducado...

If the speaker were male, he would normally say No quiero sonar maleducado.

Nosotras is the feminine form of we/us. It is used when the group is all female.

So con nosotras means with us, where us is a group of women.

If the group were mixed or all male, Spanish would usually use nosotros:

• ...fue bastante maleducado con nosotros.

It does mean to sound, and that is exactly how it is being used here.

No quiero sonar maleducada literally means I don’t want to sound rude.

In Spanish, sonar + adjective is commonly used to talk about how something comes across to other people:

• Eso suena raro = That sounds strange
• No quiero sonar arrogante = I don’t want to sound arrogant

So this is a very natural use of sonar.

Because the idea is not I don’t want to be rude, but I don’t want to come across as rude / seem rude.

Compare:

• No quiero ser maleducada = I don’t want to be rude
• No quiero sonar maleducada = I don’t want to sound rude

The second one is softer and more natural in this kind of sentence, especially when someone is about to criticize another person.

Ese means that. It points to a specific waiter, usually one already known from the situation.

• ese camarero = that waiter
• el camarero = the waiter

Using ese can make the reference more specific and a little more pointed: that waiter.

In conversation, this is very common when the speaker means a particular person from the context.

Here fue is the preterite of ser, and it presents the waiter’s rudeness as a completed event in that situation.

• fue bastante maleducado = he was quite rude

This is the most natural choice when talking about a specific incident.

Compare:

• fue maleducado = he was rude on that occasion
• era maleducado = he was a rude person / habitually rude / that was his nature
• estuvo maleducado = much less natural here; Spanish normally uses ser with maleducado

So fue fits best because the speaker is talking about one completed interaction.

Because maleducado is usually treated as a characteristic or judgment about behavior, and with this adjective Spanish normally uses ser.

So:

• fue maleducado = he was rude

Using estar with maleducado is generally not the normal choice. With many personality-type adjectives, Spanish strongly prefers ser:

• ser amable
• ser educado
• ser grosero
• ser maleducado

Even when referring to one moment, Spanish still often uses ser in the preterite:

• Fue muy amable conmigo
• Fue muy maleducado con nosotras

Here bastante means quite or rather.

So:

• bastante maleducado = quite rude

It softens the statement a little compared with something stronger like:

• muy maleducado = very rude

A useful thing to know is that bastante can mean different things depending on context:

• Tengo bastante dinero = I have enough / quite a lot of money
• Es bastante difícil = It’s quite difficult

So here it is an intensifier: quite rude.

Because with adjectives like amable, educado, grosero, or maleducado, Spanish often uses con to show the people someone’s behavior was directed toward.

• Fue maleducado con nosotras = He was rude to us

This is the normal pattern:

• Fue amable conmigo = He was kind to me
• Es muy seco con los clientes = He’s very cold with customers

In English we often say rude to someone, but Spanish commonly says maleducado con alguien.

Yes, it can be perfectly natural.

The first maleducada refers to how the speaker might sound. The second maleducado describes the waiter’s behavior.

Because the two words refer to different people and do different jobs in the sentence, the repetition does not feel wrong. In fact, it creates a neat contrast:

• I don’t want to sound rude, but he actually was rude

That said, speakers could vary the wording if they wanted:

• No quiero sonar borde, pero ese camarero fue bastante maleducado con nosotras.
• No quiero sonar maleducada, pero ese camarero fue bastante grosero con nosotras.

Yes, maleducado is common and natural in Spain.

It means someone is ill-mannered, rude, or badly brought up. In Spain, some common alternatives are:

• grosero = rude, coarse
• borde = rude, unfriendly, abrupt
• descortés = discourteous, more formal

The nuance is slightly different:

• maleducado often suggests bad manners
• grosero can sound stronger or rougher
• borde is extremely common in Spain for someone unfriendly or sharp in manner

So this sentence sounds very natural for Spain Spanish.

Because nosotras is not an indirect object here. It comes after the preposition con.

So the structure is:

• con nosotras = with us

You only use a in other constructions, for example:

• Nos habló a nosotras = He spoke to us
• Nos dio la cuenta a nosotras = He gave the bill to us

But in this sentence, con is the required preposition:

• fue maleducado con nosotras

The parts that agree in gender would change.

If the speaker were male:

• No quiero sonar maleducado...

If the group were mixed or male:

• ...con nosotros

So a male speaker talking about a mixed group would say:

• No quiero sonar maleducado, pero ese camarero fue bastante maleducado con nosotros.

If the waiter were female, you would also change:

• esa camarera fue bastante maleducada

Yes. In Spain, camarero is the standard word for waiter, and camarera for waitress.

In many parts of Latin America, you may also hear:

• mesero / mesera
• sometimes mozo / moza in certain countries

But for Spain, camarero/a is the most natural choice.

Because pero introduces a contrasting idea, and in Spanish it is normally preceded by a comma when it joins two clauses.

So this is standard punctuation:

• No quiero sonar maleducada, pero...

It works just like English:

• I don’t want to sound rude, but...

The comma helps mark the contrast between the polite introduction and the criticism that follows.