An advanced search warrior is a kind of clout-chaser on social media, most typically Twitter, who uses the advanced search function to find everything a person has ever tweeted/posted through keywords and posts it out of context in order to cast them in a bad light.
Occasionally this is done to highlight serious statements/opinions and is actually fair criticism, but it's often used dishonestly to make false comparisons in order to paint someone as a hypocrite, or just to take cheap shots at people to get loads of likes during a dog-pile, possibly not even making any sense in the process.
It often accompanies screenshots with captions like "Dis you?" or is used in L memes.
"Oh look, he's found that edgy joke I made in 2016 while I was drunk and is using it against me in an unrelated discussion, he must be an advanced search warrior."