In the effort of fairness, Twitter forgetting to trademark "Tweet" happened before Dick Costolo took the reins and began trying to turn Twitter into an actual business. However it doesn't excuse this oversight or the way Twitter is trying to get rights to the "Let Your Ad Meet Tweets" trademark that is held by none other than Twittad.
They are a 3rd party integration partner that utilizes the Twitter API to perpetuate it's pay-per-tweet advertisement model allowing users to make money off their tweets. Recently, Twitter's treatment of 3rd party integration partners hasn't exactly been conducive with maintaining healthy relationships seeing as how they pulled a lot of API tokens. Now, add suing one over their own stupidity to the list and you've got a funny, yet not very surprising situation to read and write about. The delightful details of this almost but not quite trademark dispute can be found after the break.