Occasions
Birthday shirts
Birthday shirts have a structure nothing else does: everybody gets the same shirt except one person, and that one shirt is the whole joke.
The one-shirt-different pattern
The standard move is a run of matching shirts for the group and a single different one for the person whose birthday it is. Same design language, different words. The group shirt says the crew name or the joke; the birthday shirt says the number, or the name, or the thing everybody has been calling them all year.
It works because the group photo tells the story without anybody explaining it. Generate the group design first, get it right, then generate the variant from the same prompt with the wording swapped.
Milestone numbers carry the design
Thirty, forty, fifty, sixty. A milestone number is the strongest graphic element you will ever be handed, and the temptation is to bury it under decoration. Do the opposite. Let the number be enormous and let everything else get out of its way. Bold type and vintage athletic both handle this well.
For non-milestone birthdays the number is less interesting and the joke has to carry it, so lean the other way: put the phrase first and treat the number as a small mark.
Inside jokes need context in the prompt
The generator does not know your friend. If the joke is that Marcus has been threatening to buy a boat for six years, the prompt has to say that, in those words. "Shirt for Marcus's fortieth. Running joke for six years that he is going to buy a boat and he never does. Nautical but sarcastic about it."
A prompt that just says "funny fortieth birthday shirt" will produce a funny fortieth birthday shirt for a stranger.
Write the joke out fully, including why it is funny. Nobody sees the prompt but you, and explaining it is what makes the design land.
Kids parties are a different order
For a child's birthday the run is usually small, the sizes are all youth and toddler, and the person the shirt is for cares about exactly one thing: the character, animal, color, or obsession of the moment. Say what that obsession is, say the child's age, and keep the design loud and simple. Hand drawn is usually the right style.
Parent shirts in the same design are a small addition that photographs well.
Timing
Birthdays share the problem reunions have: the date does not move. The difference is that birthday orders are usually decided late. If your party is close, tell us the date up front and we will tell you honestly whether it is achievable before you spend time on the design.
Questions
Can I order one different shirt alongside the matching ones?
Yes, and it is the most common way birthday orders are placed. Generate the group design, then generate the variant with the wording changed, and put both in the same order.
Can I put a photo of somebody on the shirt?
Not in the current version, because the design is generated from your description rather than from an upload. A described caricature often lands better than a photo anyway.
How many shirts do people usually order for a birthday?
Small runs, often eight to twenty, plus the one different shirt. Order a spare in the most common size.
Can we do surprise-party shirts without the person finding out?
Ship to whoever is organizing, not to the person having the birthday, and collect sizes in a group chat they are not in. Nothing we send is addressed to them.