If another Helldiver is behaving poorly and not following regulations, you may "Report" him/her. If you are exceptionally satisfied with another Helldiver's service you can "Commend" him/her.
In Helldivers, these reports and commends are calculated which result in a player's "Standing". If you are in "Good Standing", it signifies that you are a good example to other Helldivers. If you are in a "Bad Standing", you will be penalized and only allowed to play with other Helldivers with "Bad Standing".
Both your "Bad Standing" or "Good Standing" will deteriorate over time. This is to make sure that people with a lot of Commends can't suddenly behave ill towards others with virtually no repercussions, and that people who behaved badly should not be judged forever but have a chance to change their ways.