"Don't trust atoms, they make up everything" and "old chemists never die, they just stop reacting" are some funny chemistry sayings from Inorganic Ventures that one could put on a shirt. One of the best ways to come up with funny chemistry sayings is to take advantage of the many abbreviations in chemistry. These abbreviations often take on double meanings when viewed as everyday speech.
On the "Fun Chemistry" section of its website, Inorganic Ventures provides many chemistry themed jokes and sayings. For example, "Did you know that you can cool yourself to -273.15 degrees Celsius and still be OK?" This saying uses the abbreviation for the scientific temperature scale called Kelvin. To individuals who do not know anything about chemistry or the Kelvin scale, it will appear that the joke is saying that a person can still survive at that temperature. However, the joke does not mean OK, it means zero Kelvin, playing on the conversion ratio between Celsius and Kelvin.
This is not the only abbreviation based joke that can be made, as there are a wealth of abbreviated terms in chemistry. For example, every element on the periodic table has an abbreviation, and they often do not have anything to do with the spelling of the word. Iron is a common example of this, since its abbreviation is Fe. These can be used in a similar way as the Kelvin abbreviation to make jokes that only a chemist will understand. Putting them on a chemistry shirt is a good way to make the joke and demonstrate your knowledge of the subject.