Loss of control, ego-related conflict, relationship friction, duty and responsibility, power struggles

Having to participate in a meeting, training, holiday gathering, or other work function
Attending a funeral, wedding, or religious service because it's expected
Being required to attend anger management, rehabilitation, or another court-ordered program
Having to attend school or vocational training
Attending mandatory therapy, marriage counseling, or another mental health-related session
Having to attend Lamaze or parenting classes
Being forced to complete driver's education
Having to attend a parent-teacher conference or a meeting with school administration
Needing to attend a family or school reunion
Being required to appear for jury duty 
Having to check in with a parole officer
Being subpoenaed or given a court-appointed appearance date
Having to attend church services

Having to arrange childcare and possibly pet care
Incurring travel, lodging, and other costs to attend the event
Challenges regarding dietary needs (if the character has unusual allergies or intolerances)
Lost earnings from missing work
Putting off other plans or missing an important event
Having to put up with things the character doesn't like or finds annoying, such as long speeches, team-building exercises, or sugar-hyper kids at a family birthday party
Needing to adjust to the cultural norms of an event
Getting into an argument about politics, religion, etc.
A belligerent character being reprimanded for their behavior
Becoming intoxicated at the event
Insulting someone 
Being caught gossiping or talking trash about someone at the event
Failing to dress appropriately for the occasion 
Having to pay fees or tuition associated with the requirement
The character running into someone they don't wish to see 
Dealing with unlikeable participants or trainers