Letting someone go because they are "weird"?

Hi everyone.

A bit of context: I've just recruited my first direct report. This person is following a 2 years apprenticeship program. The goal is to permanently hire them once this program is over. In the meantime, they are spending 3 weeks in the company vs. 1 week at school until summer 2026.

The stakes are not that hight but this is my first time as a manager. I want to handle this as best as I can. So I am looking for some advices.

The interview with this person went very well, they presented well, I noticed no red flag (and I have experience as a recruiter). I wasn't alone during the interview and others had the same analysis.

Last week, they joined the team. In the span of two days, I couldn't stand even being in the same room as them anymore. Their personality was just completely different... And about 6-7 people talked to me about it in less than a week.

I addressed the issue straight away and gave some honest yet compassionate feedback (giving factual examples that I observed directly, expressed all my doubts...). This person handled the feedback so nicely that I couldn't just say "ok, whatever you are telling me, I don't care, it's over". So I told them I would give them another week but I just don't feel comfortable with them around.

They are coming back from school next week for that final week. In the meantime, I got more feedback from my team (of their behaviour when I was not around), and the more I process everything, the more determined I am. It's nothing big but a sum of little things they are doing.

It is obvious to me that I have to end their trial period.

However, my difficulty is here. I explained to them the different aspects of their posture that were bothering me (we are constantly in interaction with everyone in the company and I expressed to them clearly what I was expecting regarding their behaviour and interpersonal skills).

They answered that they could switch and correct it overnight (as an example, they are very negative about everything. After two days in the company, they told me that the way my department is organised is horrendous - when it is objectively not true given the circumstances that they knew about, and they barely have a real job experience).

They clearly are making some efforts since that feedback I gave, but it doesn't feel natural at all. Overall, they are just "weird" (several people just felt uncomfortable being next to them and talking to them).

I do not know how to terminate their trial period, given that they are making effort but I just do not feel comfortable with them. I do not want to hurt them, and their personality is what it is, but it doesn't match the vibe and the posture expected. I do not know how to express that in a good way.

Sorry it's a lot, I'll be happy to provide you with more context if needed, I wrote this as it was coming.

Thank you for your time.

PS- please bear with me as English is not my main language.

Edit: I am giving here more context and some examples, as some comments pointed out it was needed (I agree).

First thing I want to share is that this person is older than me and I might expect more from them when it comes to their behaviour than if they were just 18-20. I understand this is probably a bias that I have.

As for examples:

• on their second day, they were trying and share with me details of their love life (my date was awful, I have a next one tomorrow, I hope I will get laid it's been a while....). Oh and they added "be prepared because I love to talk about me and my life".
• when I introduced them to different people they will be working with, they always made a comment about how they would do their job and that they already know that from school. Example: they told the security manager how the fire safety should be dealt with and that they should get back to work and not to lose anymore time. They could share their insight if needed. The safety manager has 20+ years of experience.
• they made a comment about my coworkers weight and how they should manage their sugar intake when they were minding their own business eating a cake for desert and not talking about it.
• another employee was visiting my coworkers office to share about something that they had no business with. They heard some key words, stood up and went in front of the door to listen what was said and then told me about it (which I addressed as well by not being ok).
• for their onboarding, I slowly showed them about a tool. They asked me if they could try and realise one task. I was very ok with this, gave them a few keys and gave them the space to get familiar with the tools and the task. After successfully doing it, and me praising them for it, they told me "I think I get everything about this job now. Wow, what am I gonna do in 3 months ? I'll be bored". Before this (during the interview and on their fist week), I presented them all the missions that will be explored with my support. This was far from being it.
• one day when I was not around for a couple hours, they went to ask a question to my coworkers as I told them they could always do that in case they need anything, information... They asked a question, and while my coworker was looking up for the answer in some files, they said "finally I got you stuck on something! I reached my goal".

Overall, they behave like they know it all (correct people in the middle of a conversation they were not part of - using Google to grammar check them).

They only engage in conversation to either correct people or if we ask question about themselves.

I have other examples but I think this might help understand what I mean.

Right here, I am wondering if this behaviour is manageable, if it worth it to coach that person or if I will just be loosing my time. I totally understand people have their own set of skills, and everyone has room for improvement but this just doesn't feel right. They are even mean sometimes and this looks toxic to me.

I feel "betrayed" as this behaviour is not what they showed and communicate during the interview.