Opposite Day is not an official holiday recognized by any government or organization. However, it is a playful and tongue-in-cheek observance that some people use to have fun and think creatively. Opposite Day is celebrated by doing the opposite of what is expected or doing things in a way that is opposite to the norm. So, when it comes to gift giving, it's an opportunity to think outside the box and come up with unique and unexpected gift ideas.

One popular gift idea for Opposite Day is an "anti-gift". Instead of giving a physical gift, you can give an experience or an activity that goes against the norm. For example, if the person is a clean freak, you can give them a day of messy fun like a pottery class, or if the person is a night owl, you can give them a gift certificate for a sunrise hot air balloon ride.

Another great gift idea is a "reverse gift". Instead of giving something new, you can give something that has been used, repurposed or recycled. For example, you can give a vintage piece of jewelry, a handmade quilt made out of old t-shirts, or a terrarium made out of recycled materials.

A "backwards gift" is also a great idea. Instead of giving something that is typically used in one way, you can give something that can be used in the opposite way. For example, you can give a book that can be read backwards, a clock that runs counterclockwise, or a shirt that can be worn inside out.

For the prankster, a "fake gift" can be a great idea. Instead of giving a real gift, you can give something that appears to be a gift, but it's not. For example, you can give a box of rocks wrapped in gift paper, or a "gift certificate" for a non-existent service.

In conclusion, Opposite Day is a playful and tongue-in-cheek observance that provides an opportunity to think creatively and come up with unique and unexpected gift ideas. Instead of giving traditional gifts, you can give "anti-gifts", "reverse gifts", "backwards gifts" or "fake gifts" to surprise and delight the person. These gift ideas are a great way to have fun and to show that you put thought and effort into choosing the perfect gift. It's important to keep in mind that Opposite Day is meant to be light-hearted and fun, so be sure to choose a gift that is appropriate and will be received in the spirit of playfulness.