There are certain indisputable truths in this world: the sun rises in the east and sets in the west; the Earth rotates around the sun; and the youngest child is the best, most wonderful person in the family. These are facts people, and you can't argue with facts especially when accompanied by GIFs—everyone knows GIFs are the TRUTH.
Warning: Below you may find some deep truths about my own childhood and clear reasons I need therapy.
Your parents always say what a good baby you were. This is because they had no idea what was going on with the first one, so you just seemed easier. But still, you can always say, "I was SUCH a good baby"—and smirk at your siblings at Thanksgiving.
2. If your mother breastfed, you were probably fed for longer. Why? Because you were the last one and she really wanted to, uh, milk it.
3. You were probably an accident. You may or may not know this, but if your mother says things like, "You were such surprise!" you were definitely an accident. But a happy accident, so quit crying, baby.
4. You think you were adopted. Largely because your siblings kept telling you you were adopted and/or you have red hair and no one else has red hair.
5. Your stupid siblings are in every picture with you. You never got to shine on your own. Never.
6. Your parents thought it was fine to send you to sleep away camp at age 6, because your brother and sister were there. It was not fine. There was a lot of crying. A lot.
7. In the early days of television there was no remote, except for you. You were the remote.
8. You were tickled until you peed your pants. Then you were made fun of for peeing your pants and unrelated bedwetting. Obviously, it wasn't your fault—they were tickling the piss out of you. But the bedwetting thing, well, that was on you, but they didn't have to be such jerks about it.
9. You repeated a lot of curse words like a little parrot. And it was f&^#ing adorable.
10. Your parents always called you either your brother's or sister's name (or a dreadful combination of both). They still do this, even if you are now in your mid-thirties.
11. You always feel so young because your siblings are older than you. You're still basking in your glorious 30s while they are practically out to pasture in their 40s. Same will go for your 40s and 50s and so on down the line.
12. If your siblings were much older than you and were out of the house when you were young, you also had the experience of being an only child. And it was wonderful. This is particularly helpful if you have decided to have only one child, since you secretly think having siblings is overrated.