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

Because maleducada agrees with the speaker.

If a woman is speaking, she says maleducada.
If a man is speaking, he would normally say maleducado:

• No quiero sonar maleducada = said by a woman
• No quiero sonar maleducado = said by a man

The adjective changes to match the person who is supposedly sounding rude.

Yes. Sonar here works very much like English to sound.

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

It means the speaker does not want to give that impression. It does not necessarily mean she is rude; only that she does not want to seem rude.

Other similar examples:

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

Because sonar maleducada and ser maleducada are not the same.

• sonar maleducada = to seem / come across as rude
• ser maleducada = to be rude

In this sentence, the speaker is being careful: she wants to express an opinion without appearing impolite. So sonar is more natural than ser.

Spanish demonstratives show distance, not only physical but sometimes emotional.

• este = this
• ese = that
• aquel = that over there

In ese camarero, ese points to a waiter who is a little more removed from the speaker, or simply one already identified in the situation. In many contexts, ese can also create a slight distancing tone, a bit like that waiter in English.

So ese camarero here is very natural.

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

• ese camarero fue bastante maleducado = that waiter was quite rude on that occasion

If you said era bastante maleducado, it would sound more like a description of his general character or habitual behaviour.

So the contrast is roughly:

• fue = he was rude that time / in that situation
• era = he was a rude person in general / habitually

Yes, you may hear that, and it can sound natural in some contexts, but fue maleducado is very common when talking about someone’s behaviour in a particular incident.

A helpful rough distinction is:

• fue maleducado = he behaved rudely / he was rude in that event
• estuvo maleducado = he was being rude at that moment

In everyday use, the line is not always strict, but fue maleducado is a very standard choice here.

Here bastante means quite, rather, or fairly.

• bastante maleducado = quite rude

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

• muy maleducado = very rude

So the speaker is not saying the waiter was just a little rude, but also not making the strongest possible statement.

Also, in this sentence bastante is an adverb, so it does not change form:

• bastante maleducado
• bastante maleducada

It stays bastante either way.

Because with maleducado, Spanish commonly uses con to indicate the person someone behaved rudely toward.

• Fue maleducado con la clienta = He was rude to the customer

This is one of those combinations you largely have to learn as a pattern:

• ser amable con alguien = to be kind to someone
• ser antipático con alguien = to be unpleasant to someone
• ser maleducado con alguien = to be rude to someone

English often uses to, but Spanish often uses con in these cases.

Because clienta is the feminine form of cliente when referring to a female customer.

• el cliente = the male customer / the customer in a generic masculine sense
• la clienta = the female customer

So since the sentence refers to a woman, la clienta is the appropriate form.

In modern usage, you may sometimes hear la cliente too, depending on region or preference, but la clienta is very common and completely standard.

It is a very good and very common word, especially for someone who is impolite or ill-mannered.

In Spain, some related words are:

• maleducado = rude, ill-mannered
• grosero = rude, coarse, vulgar
• borde = rude, unfriendly, sharp in manner

So:

• maleducado often focuses on bad manners
• grosero can sound stronger or coarser
• borde is very common in Spain for someone who is abrupt or unpleasant

In this sentence, maleducado fits very well.

Because pero introduces a contrast, and in Spanish it is normal to place a comma before it when it links two clauses.

• No quiero sonar maleducada, pero ese camarero fue bastante maleducado con la clienta.

This is similar to English:

• I don’t want to sound rude, but...

So the comma is standard punctuation here.

Yes. It is a very common softening structure.

• No quiero sonar maleducada, pero...
• No quiero ser injusta, pero...
• No quiero exagerar, pero...

The speaker is preparing the listener for criticism while trying to sound polite or careful. In real conversation, this often signals: I’m about to say something negative, but I want to say it tactfully.

Not really. It is a normal conversational strategy.

The speaker is not saying that calling someone rude is itself rude; she is showing caution before making a negative judgement. In English we do the same:

• I don’t want to sound rude, but that waiter was quite rude to the customer.

So the first part softens the criticism, and the second part gives the opinion.