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).
Oh wow this brings back memories. More than a decade ago I lived in shared housing where each room has its own telephone port. The idea was every person was supposed to get their own internet. But after a few months of troubleshooting my housemates' internet issues I decided to open up my wifi to everyone else. I used Chillidog, a captive portal software that runs on ddwrt. I had a 3 hour continuous-use limit, after which weird stuff would happen to their images like being turned upsidedown or blurred. I used this very site to make it happen!
Eventually, my housemates just contributed to my internet bill and dropped their own subscriptions. I got rid of the captive portal and went with something more traditional
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.