DIY Kissing Booth Costume: Find a box that is about as wide as your shoulders, and long enough to reach from the top of your head to your waist. Cut out squares for your arms, and then a larger square for your head/torso along the front. Then staple some fabric along the sides like in the photo, and add a sign to the front that says, "Kissing Booth". Get a friend to put some red lipstick on and have them kiss you several times on your face and you're done.
Alternatively, you can get a hoola hoop and attach two pieces of string to it to wear over your shoulders like in this kissing booth costume (Buy Direct), and then attach a piece of fabric around the hoop. Write your 'fees' for a kiss on the outside, cover your face with kisses again, and add final touches with heart-shaped finds from the dollar store.
Some more ideas to round out your kissing booth costume: