I work in a single large office with 6 other people. Amongst us, there is one guy who constantly talks a lot about total bullshit. Due to flexible working schedule, we can start and finish work whenever we want, as long as we get the job done.

What is usually happening is that the guy spends most of the time during the 10AM - 4PM hours talking, wasting time and distracting others. He then stays over for a few hours after work to actually finish what he is meant to be doing. He has no life and no other activities from what I know and thus spends most of his time wasting it on bullshit like this.

The problem is that me and others from the office, prefer to get the job done during the day so we have time for life later on. Clearly a mismatch here...

My question is, how do I proceed to slowly but consequently shut him up? I'd rather avoid any HR action as our group has a really good dynamic between ourselves and I don't want to introduce toxicity. Nobody really brought the issue up yet but it is clear that everyone tries to cut short any conversations with him and stays with headphones on most of the day.

I can easily talk to him in private about it. The issue is that he is sort-of my boss (he trained me at some point) and has good connections in the upper management. From one point of view, I want peace and quiet and some form of decent working conditions but from another, I don't want to shit where I eat as the job is a crucial point in the career I want, at least for the next few years.

Any ideas fellas?