The most common and most likely answer to this crossword clue is the 4 plus 3 plus 4 letter word LOSE THE PLOT
I've seen this crossword clue in The Guardian
L
O
S
E
T
H
E
P
L
O
T
More clues leading to the result LOSE THE PLOT
Buddy explains!
The straight part
We know that "Rant and rave" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rant and rave = lose the plot.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.