They're just looking at each other but you already know: I SHIP IT!
Every time you and your friends meet you can wear this shirt. Imagine being in a group of three. Your male and female best friend. You always hang out and chill, but they sometimes feel so close to each other than they're with you. You point at your tee and say: "I ship it".
The next time you meet, they tell you that they're in a relationship now! Congratulatyions you just made two people happy and yourself a third wheel :/ But at least you got a nice shirt! :D