The most common and most likely answer to this crossword clue is the 5 letter word DIPPY
D
I
P
P
Y
More clues leading to the result DIPPY
Buddy explains!

The straight part
We know that "Crazy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case crazy = dippy.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.
What does DIPPY mean?
DIPPY adjective- Lacking common sense.
- Having romantic feelings for; excited or enthusiastic about.
- Of an egg: cooked so that the yolk remains runny and can be used for dipping.
- Involving or suited to dipping.