It's safe to say that on more than one occasion, I've seen people do and say things in a volunteer capacity that I cannot imagine they would dare replicate in their business setting. Chronic absence without notification, lack of accountability, inappropriate tone with fellow committee members, and the ever-popular "you're just lucky I'm sitting here" attitude aren't going to propel you to success at work or do anything for your reputation as a volunteer either! Your volunteer roles and contributions are an extension of your personal brand. A great volunteer contributor can become a sought-after resource by his/her fellow professionals. Conversely, an unwise volunteer that acts unprofessionally will quickly gain a reputation as the person nobody wants on their committee - or in their office. Trust me!
If a volunteer placement is making you act out of character (to put it nicely), then it's very likely that the simple solution is to find another role better suited for you. Alternatively, if you love your volunteer role and it has the potential to let you shine and grow your skillsets - then knock it out of the park! You never know who might be watching and taking note.
PS - if you're just having a bad mood day, here are some tips to shake it off before you join your volunteer meeting.