Bench Tails is a Meme in which a character is sitting on a Bench with a smile on their face, arms relaxed against the back of the seat and their legs spread open. This alludes to a scene in an infamous comic in which Tails (Sonic) is sitting on a bench in that same manner, looking over two young characters from the Sonic (Series) franchise.
Characters featured in this meme are given the connotation that they're into infants.