If you are communicating on an Issue or PR, you might be met with "ACK"s and "NACK"s (or even "approach (N)ACK" or similar). ACK, or "acknowledge" generally means that the commenter approves with what is being discussed previously. NACK means they tend to not approve.
What should you do if your PR is met with NACKs or a mixture of ACKs and NACKs? Again there are no hard rules but generally you should try to consider all feedback as constructive criticism. This can feel hard when veteran contributors appear to drop by and with a single "NACK" shoot down your idea, but in reality it presents a good moment to pause and reflect on why someone is not agreeing with the path forward you have presented.
Although there are again no hard "rules" or "measurement" systems regarding (N)ACKs, maintainers — who’s job it is to measure whether a change has consensus before merging — will often use their discretion to attribute more weight behind the (N)ACKs of contributors that they feel have a good understanding of the codebase in this area.
This makes sense for many reasons, but lets imagine the extreme scenario where members of a Reddit/Twitter thread (or other group) all "brigade" a certain pull request on GitHub, filling it with tens or even hundreds of NACKs… In this scenario it makes sense for a maintainer to somewhat reduce the weighting of these NACKs vs the (N)ACKs of regular contributors:
We are not sure which members of this brigade:
Know how to code and with what competency
Are familiar with the Bitcoin Core codebase
Understand the impact and repercussions of the change
Whereas we can be more sure that regular contributors and those respondents who are providing additional rationale in addition to their (N)ACK, have some understanding of this nature. Therefore it makes sense that we should weight regular contributors' responses, and those with additional compelling rationale, more heavily than GitHub accounts created yesterday which reply with a single word (N)ACK.
From this extreme example we can then use a sliding scale to the other extreme where, if a proven expert in this area is providing a lone (N)ACK to a change, that we should perhaps step back and consider this more carefully.
Does this mean that your views as a new contributor are likely to be ignored? No!! However it might mean that you might like to include rationale in any ACK/NACK comments you leave on PRs, to give more credence to your views.
When others are (N)ACK-ing your work, you should not feel discouraged because they have been around longer than you. If they have not left rationale for the comment, then you should ask them for it. If they have left rationale but you disagree, then you can politely state your reasons for disagreement.
In terms of choosing a tone, the best thing to do it to participate in PR review for a while and observe the tone used in public when discussing changes.