"Let's play" videos are a hugely popular online genre in which gamers narrate their playthroughs of games that excite and challenge them.
In October 2015, Sony filed a trademark application for the phrase in a nondescript typeset font, covering "Electronic transmission and streaming of video games via global and local computer networks; streaming of audio, visual, and audiovisual material via global and local computer networks." In other words, the exact common, generic use.
This is a bullshit move of staggering chutzpah. It is exactly the kind of thing that trademark doesn't cover. Trademark is supposed to help consumers tell which company is making which commercial offer: if Sony were synonymous with "Let's Play" (or if they'd made up a phrase they hoped to become synonymous with), trademark would help viewers know that when they saw or heard the trademark, it was coming from the source they assumed it originated with.
But taking a generic term (given that a judge already found "Best Buy" to be too generic for broad trademark enforcement, "let's play" certainly qualifies as generic) and then attempting to get the government to issue a title deed on it for your multinational corporation is theft of language, stealing the words right out of our mouths. If I had my way, any lawyer who put their name to one of these applications would lose their Bar card.