I am so sure someone has already done still it is always something fun to do. So basically you make a statement of some sort, which would look good on a t-shirt. The statement/quote can be funny, sad or whatever. If you want you can add in a story or something behind the t-shirt line.

An example "I fought Tiamat for 6 hours and all I got was this stupid Fire Crystal"

In 2006? SE released Wing of the goddess expansion and with it came this Large Dragon; it was a pain in the butt to get to its spawn location as monsters along the path detected by sound and could instant kill a level 75 mage at the time. Fighting the dragon was a pain in the butt and then the drops were random. I have heard that Tiamat has even dropped no items before.

Some Fun info about Tiamat
Around 100,000HP
Killable by: 36+ characters at level 75
Special Attacks: Draw-In, Mighty Strikes (multiple times), Auto-Regen (around 200HP/tic), Blaze Spikes, Firaga III
Spawns around E-9 every 3-5 days. (24-72hr after maintenance)

I truly do miss this stuff challenging stuff though.