Meet in a bad mood (5)
I believe the answer is:
cross
'meet' is the definition.
(crossing is a kind of meeting)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cross that I've seen before include "Thwart, oppose" , "Your adversary here" , "Traverse - displeased" , "Peeved" , "means of execution" .)