#mcchicken is trending because of a new chicken sandwich from McDonald's. The sandwich is made up of a grilled chicken patty, bacon, and cheese. It also comes with lettuce and mayonnaise on a toasted brioche bun. The sandwich was first tested in select markets in April, but it is now being rolled out nationwide. It is currently available for $4.49 at most McDonald's locations. The #mcchicken hashtag has been used more than 100,000 times since the announcement of the new product on Wednesday evening.