Not causing a scene at the funeral is a good etiquette rule to follow. If this person approaches you, you may say, Excuse me, and walk away, purposefully, but without any show of anger as if you were called off to deal with something urgent. You can go to the bathroom for a minute if need be. Miss Manners is indifferent so long as it convinces anyone watching that your departure was unrelated to the person.
When you bite your tongue repeatedly, underneath it may feel like you are avoiding conflict, but often you're actually building up resentment. We all know that the 'bottle it up and implode or explode later' plan does not work well for any of us. Every unspoken thought becomes a brick in the wall that grows between you and the other person.