It depends on where you are and what you're doing.
If you're in a public swimming pool you're fairly safe. Just watch the bubbles rise and say ' What a wonderful creation.' Or, ' After my butterfly, I watch the methane rise.' Something like that.
If you're in a fancy restaurant and your fart is audible and carries a detectable scent (stinks like hell) you'll have to do the gentlemanly thing and either own up, mea culpa, and say 'That was good but it wasn't one of my best. I can do better.' Or say ' Mother Nature calling. A country package is on its way!'
If you're being awarded a certificate or diploma then you can just ignore the fart, smile and walk on.
If you're being introduced to a beautiful man or woman or figure of note, celebrity, royalty, wealthy person, etc etc, and you happen to let out an absolute gem just say ' Sorry , I was educated in Australia.' Everyone will understand.