Personalized Stays At My Birthday Party T-Shirt. Funny birthday T-Shirt - Vintage Black with Las Vegas parody, party hat and balloons, says WHAT HAPPENS AT MY BIRTHDAY PARTY STAYS AT MY BIRTHDAY PARTY! Everyone loves our Custom T-Shirts! Wardrobe essential for looking good, 24/7. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar. Shoulder-to-shoulder taping. Double-needle stitched sleeves, bottom hem and front neck. Note: greys are a cotton/polyester blend.