Question: A friend of a friend has on multiple occasions aggressively asked how my self-study for software engineering interviews is going. Most recently I answered very briefly, because I find it too nosy and the person to be arrogant and presumptuous. I don't like for example that he's convinced that I seem too calm about the job interview preparation process and that I don't push myself hard enough.

Initially I just listened to him rant over the phone, and after he realized he was doing all the talking he then asked for my input and I answered honestly. Then he would "check in" with me over Messenger or when I ran into him at a party it would be the first topic of conversation. Since he didn't change, one thing I did when he was doing the same to someone else right in front of me was I asked "What do you mean?" and he simply acknowledged he was rambling. I've been distancing myself from him as of late which is tricky since he's in a few of my friend groups - I have no desire to "win."

How do I convey that I'm not interested in him essentially interrogating me and opining in career-related matters?

Answer: 
It sounds like you have already figured out this person's *motivation* for asking you questions - they want to give you advice. "Advice-giver" is a [recognised personality trait](https://www.psychologytoday.com/gb/blog/evolution-the-self/201308/what-you-should-know-about-advice-givers), and many do it for their own ego gratification.

As the opportunity to give advice is evidently what is prompting the questions, if you stop fuelling him by answering them, the advice will hopefully stop.

[This article](https://www.psychologytoday.com/gb/blog/fulfillment-any-age/201506/9-ways-handle-nosy-people) on Psychology Today suggests various ways of dealing with nosy people. Two of those ways are:

1. **Tell the truth**  

This could be the best approach if you don't want to be rude to the person. Answer their questions, but severely limit what you tell them. If they ask how it is going, you could just say "*it's going great, thanks*". Give yes/no answers to their questions if you think that will cut him short. If he persists then you could cut it short by saying something like "*that's a lot of questions, shall we talk about something else?*"
2. **Deflection**
If you are comfortable being more direct in telling them that you don't want to talk about this, this approach is about not answering any questions at all. Change the subject - perhaps say "*I'm bored with study, I'd rather talk about something else"*.

Other techniques include stating your discomfort about the questions, but that may send the message that your self-study is not going too well, and that may not be the message you want to send.

Ultimately though, not allowing an 'advice-giver' to give you advice is like starving them of their oxygen. They will not be interested in pursuing you for answers if they aren't getting what they want out of it.
From the way you describe it in your question, it sounds to me like you're already dealing with the situation perfectly well.

As you yourself have said: you let them ramble on, you were honest with them when asked for feedback, then later you distanced yourself from them.

It sounds like you have already "convey[ed] that [you're] not interested in him essentially interrogating [you] and opining in career-related matters".

It also sounds like this person is just one of the many random people you'll run into in your life. This guy could be an arrogant loudmouth, or he could be clumsily and unsuccessfully trying to make friends; we can't know.

In short: keep on doing what you're doing - he'll get the message and leave you alone.

If you don't feel that's good enough - that you've already tried the polite approach - then you can more forcefully reiterate your disinterest, or simply ignore them and go and talk to someone else. 
You're not obliged to entertain every person who wants to talk at you, after all.