The joke has to survive being overheard
A two-person joke printed large becomes a private thing worn in public. The ones that work read as an ordinary line to strangers and as a specific memory to exactly one person.

PROBABLY FINE. To anyone who sees it on the street, that's a dry two-word slogan of the kind that has existed forever.
To one person it's what somebody said, in a particular voice, while something was very obviously not fine. That gap is the whole gift.
What makes a two-person joke different from a team one?
The audience ratio, and it changes the design.
A team in-joke is worn among the people who get it — at the office, at the offsite, in the group photo. Most of its viewings are with the in-group present.
A gift between two people is worn everywhere except around the person who gets it. It goes to the shops, to work, to their mother's house. So the shirt spends most of its life being read by people who have no idea, which means the line has to work as an ordinary garment on its own.
What does that rule out?
Anything that reads as a fragment.
A shirt saying THE THING WITH THE BOAT announces that there is a story and doesn't tell it,
which puts the wearer in the position of either explaining it forty times or looking like they're
withholding. Same for a date, a set of initials, a number with no context — those read as
memorial, and they invite questions.
The test is simple and worth applying honestly: would a stranger think this is a normal shirt? If yes, it's wearable. If it makes them ask, the wearer has been given a chore.
So what kind of phrase works?
One that's already plausible as a generic line.
The good candidates are things that sound like they could be printed on any shirt anywhere: probably fine, no notes, allegedly, it's a process, back by Tuesday. Each of them is a perfectly normal thing to see on a garment, and each of them can be the exact sentence somebody said on a specific afternoon.
You're looking for the overlap between a phrase from your life and a phrase that reads as generic. The joke lives in the overlap, and nobody outside it notices anything.
Does the design need to be plain?
Usually, and for the same reason.
A quiet setting — plain heavy capitals, one colour, centred — makes it look like a designed statement tee. Elaborate treatment draws attention to the words, which is the opposite of what a private line wants.
There's an exception worth knowing: if the joke is about something visual — a specific object, a badly drawn thing somebody sent — then rendering that faithfully is the joke, and it can be as elaborate as it needs to be.
What if the joke needs a picture?
Then draw the object plainly and let it be ambiguous.
A specific chair, a specific sandwich, a badly parked car, drawn as a clean line illustration, reads as a nice minimal graphic to strangers and as one very particular incident to one person. That's the same double reading, arriving through an image rather than a phrase — the way a Valentine's design can be a table for two.
The rule that carries over: it should be a complete image, not a reference to a missing one.
Is there a risk of it being cruel?
Yes, and it's worth checking before printing rather than after.
A joke about somebody is different from a joke with them, and a garment makes the difference permanent and public. If the line is about a time they were embarrassed, a habit they're self-conscious about, or a thing they'd rather not have commemorated on cotton, it's a joke they're the object of rather than a participant in.
The version that works has them as the co-author. They said the line, or they were there when it happened, and the shirt is proof somebody remembered.
How long do these last?
Longer than a team joke, because there's nothing to expire.
A team in-joke has a shelf life — people leave, the context dissolves, and by next year half the office doesn't know. A two-person joke has an audience of two and both of them still remember, so the shirt keeps working for as long as the friendship does.
Which makes this one of the few designs where longevity comes free.
How do I get one made?
Give the line at JustOG — the exact words, and say it should be set plainly. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.
Designs other people have published are in the shop.
Everyone else reads a slogan. One person hears a voice.