Bros Night refers to an episode format on The First Podcast, initially planned as a roughly "fortnightly experience" (twice per month) but in practice occurring very occasionally when everyone is available for it, where Lars, Joe, Ohan and Richard sit down to discuss a variety of nerdy topics with no particular agenda.
The framework for Bros Night first came about on an early episode, in which Richard was the featured guest. Lars made an executive decision to invite previous guest Ohan Ghazarian to sit in as a guest host, with Chris participating in the background as something of a moderator.
This turned out to be what Lars and Joe considered an exceptional format, with the four (and a half) participants all playing very well off of each other. This opinion was shared again on a later episode, where Richard and Ohan actually filled in for Joe during the first 45 minutes (after which Joe came into the call, followed shortly by Chris again).
Lars and Joe agreed to start featuring Ohan and Richard as regulars on this new episode format, which is something of an "evolution" of the old episode style (as in, the latter two would be considered guest hosts, not formal guests, and the discussion would be organic).
As the notability of guests went up, Bros Night episodes started becoming fewer and far between. While still happening, it has become more difficult to get all four people available at the same time (especially Lars and Joe).
Chris was quietly dropped as a requirement for these episodes, as he suffers from notoriously poor wireless internet, does not have a big enough following to justify the expense of an additional audio track, and largely had little to say on the episodes as it was. The other boys wish him well and have expressed interest in re-introducing him if his situation changes.
Possible spin-off? Edit
Lars has occasionally noted that he could have seen this format of the show being the show if certain events had played out differently. There have been talks once in a while about doing a spin-off podcast with this format and these hosts, but the spare time to do so has all but evaporated in the modern era.