I thought it would be cheeky and fun to buy him a risque card from an adult boutique, thinking everyone would get a good laugh, and we'd have something to roast the young man with.

Why would you even want to roast a just-turned-18-year-old anyway? Get the young person something relatively humorous about being unleashed onto an unprepared world and and cheer them on, not roast them. Ugh.