The more fun thing to do is to manipulate messages in transport.

There was a really fun game where you could join public wifi and change every image request response to be images of cats instead. (by changing the requesting URL and/or response).

This idea was borne from the 'upside-down-ternet' which people ran on their Guest Networks. (https://www.ex-parrot.com/pete/upside-down-ternet.html)

Would be fun to have a word replace running for "Thank You" to "Fuck You", it's not at all impossible to do.