The most common and most likely answer to this crossword clue is the 4 plus 2 letter word DEJA VU
I've seen this crossword clue in Financial Times
D
E
J
A
V
U
More clues leading to the result DEJA VU
- It’s not really a souvenir of the Parisian experience
- Poor Jude, concealing a very familiar feeling
- Initially dismiss everything just as very unusual and weird sensation
- Light a master of sci-fi briefly recalled that seems familiar
- Outsiders who decolonize Java and Vanuatu, strangely seen before
- Pairs of deeply jaded vulgarians offering tired stuff
- Familiar feeling due to doctor drinking endless coffee
- Familiar sensation of French getting German agreement to rising radiation
- Strange phenomenon of second sight?
- Outsiders to decolonise Java and Vanuatu, strangely familiar phenomenon
Buddy explains!

The straight part
We know that "tired stuff" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tired stuff = deja vu.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.