If I found a bank that let me have 11.8 million other (non spouse) people on it and put $1 in that account would I be liable for paying gift tax?
This is a "reductio ad absurdum" of the fact that joint accounts are considered "gifts" for the purposes of the gift tax.
Under U.S. law, each donor can give up to $15,000 per person, per year to as many people as desired gift tax free (this is called the "annual exclusion").
So, you could make a gift like this without owing gift tax or having to file a gift tax return on IRS Form 709.
The gift tax portion of the Internal Revenue Code is specifically designed so that de minimis gifts don't have to be accounted for.
Also, the amount of the gift for gift tax purposes if you had 11.8 million co-owners of an account would be 1/11,800,000 dollars, not $1 dollar each. While co-ownership of a joint account is a gift, it is not a gift of 100% of the value of the co-owned account to each co-owner.
The default rule in absence of evidence to the contrary, is that co-owners of property have equal ownership of it. Adding one joint owner to a solo account is a gift of half of the amount in the account.
