No, it isn't rude to show up without a gift for your hostess. However, it is important to consider the circumstances surrounding the event. For example, a casual pizza night at a friend's house might not warrant a gift. On the other hand, housewarmings, birthdays, or bigger celebrations present excellent opportunities for home or food gifts. Post explains that most people feel like they are a burden when being invited to an event and that a hostess gift eases the "guest guilt" that they experience. However, you never have to present a gift to someone to feel welcome into their home or special occasion because you were asked to attend for a reason.