1
general::
Phrase(s): hot under the collar
Fig. very angry. • The boss was really hot under the collar when you told him you lost the contract. • I get hot under the collar every time I think about it.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Angry, as in She is quick to get hot under the collar, but once the problem is ironed out she forgets it entirely. This expression alludes to the heat of anger. [c. 1900]
American Heritage Idioms