Risks involved choosing my own seed mnemonic? I reading that 'humans are bad at randomness' and one should always let an algorithm choose your seed for you.

While I agree that maybe it's not advised to make my brain wallet 'zoo' x 23 + checksum as an easy to remember phrase, but besides the obvious, what real risks are there to choosing your own seed?

I've also read that if you use the date as your seed's seed (akward phrase, the seed of the random function that my nmemonic seed is created from) then if that is known by an attacker they can use that to crack my wallet really easily.

What else could go wrong? for instance if i decide to use all the food words out the list, but change 1 of those to an easy to remember alternative, then I've a bunch of food words and one randomly out of place non-food word (seams ok to me). Are there brute force algorithms that could take advantage of that?
The BIP39 word list consists of 2048 words.

For a regular, 24 word mnemonic, you have: 2048^23 ways to arrange the non checksummed words. At 1 trillion combinations per second, this would take you  ≈ 3.3×10^46 times the age of the universe to compute, even before you bother checking the checksum options.

Now, let's say that out of these 2048 words, 500 are food items (this is an illustrative example, I haven't actually counted them). Now, your combinations are some combination of 22 items (possibly repeating) from those 500, plus a random word from the 2048.

This evaluates as 500^22 * 2048 * 21. At 1 trillion combinations per second, this would take you ≈ 2.4×10^46 times the age of the universe to compute. While this is still an extremely large number, it is still nearly 30% less than the initial case, which is a non-trivial loss of entropy.

Moreover, if an attacker is able to discover even a few words from your mnemonic (maybe a friend peaked at it while visiting, or you entered a fragment into a scammy wallet before catching on, or any number of other scenarios), your possible combinations go down extremely fast. Even a perceived small loss of entropy can mean the difference between being brute forceable after 6 known words and being brute forceable after 19 known words.

In 2019, with access to reliable entropy generation in nearly every device, it is simply not worth it to attempt to come up with convoluted schemes.