Tense expression of annoyance when restricted by employee of poor quality (5-4)
I believe the answer is:
Here is my best explanation:
'of poor quality' is the definition.
'tense expression of annoyance when restricted by employee' is the wordplay.
'tense' becomes 't' (abbreviation used in many dictionaries).
'expression of annoyance' becomes 'drat'.
'when restricted by' indicates putting letters inside.
'employee' becomes 'hire'.
'drat' inserted inside 'hire' is 'hirdrate'.
(Other definitions for third-rate that I've seen before include "Very inferior in quality, using ordinal number", "Very inferior in quality in numeric description", "Of very poor quality", "Very inferior in numerical way", "Very inderior in quality - do a count", "Inferior" and "Very inferior in quality - count down".)