The Scrabble board is a 15-by-15 grid, so naturally, Scrabble dictionaries have no need for words longer than 15 letters. Oddly even "Super Scrabble" which is Scrabble played on a larger board and with more tiles, still uses the 15-letter limit.
Some 16-letter words for your consideration:
I can totally see someone staring off with "clocks" in their grid, turning it into "clockwise", and then in a brilliant burst of insight, combining it with "count" and some stray tiles to make "counterclockwise". If I ever pulled that off, I would be so proud that I wouldn't even care if I won the game. (OK, I'd still care, but either way it would be awesome.)
What is the longest word that you have ever used in a Bananagrams match? For those who like games with rounds that escalate, the must-contain-an-N-letter-word would be an interesting and challenging variation. How high can you go?