Recently I acheived the 'Completionist' badge when I marked my 113th drama as completed. This is an arbritary number and very much don't believe other people achieved this badge at this exact point. I had marked so many dramas as 'dropped' right before achieving this badge, so it didn't have anything to do with 'completing a lot of dramas in a row'. I think daily dynamo is an equally "random" badge as I've logged in many months every day and have yet to achieve, and commentator might also be random.
HOWEVER, gift giving and flowers have certain definitive checkmarks.
'Gift Giver' badge I didn't note but I am guessing its from sending 25 gift awards
'Thoughtful' badge I think was from sending 50 gift awards, and
'Generous' was from sending 100 gift awards.
It took me 2 years of working towards it, to find out that the 'Bouquet Sender' Badge was from sending 30k flowers total.
If I recall correctly, the 'Flower Sender' badge was allocated from sending 10k flowers total.
So some of these badges (like gift giving and flower sending) have definitive checkmarks, while others badges might be allocated at random times.