I am tired, so I will beg off the party tonight.
beg off
idiomTo obtain somebody's permission to skip or cancel an event that one has previously arranged with them.
Origin
disputed originbeg + off
She had to beg off the dinner invitation because she suddenly felt unwell after work.
Although he had initially promised to attend the gala, he decided to beg off at the last minute to avoid the inevitable confrontation with his former business partner.