People get evil, yes every time while someone's doing a victory pose.
I prefer to watch from a side when someone has better plans to ruin one's photograph, unless he tries this cheesy thing with me, grrr.
Though grannies & kiddos are pro in this section. Can't blame, they do it unintentionally! But it's still illegal & I'd call it photobombing in Urban Dictionary's words.
I'm sharing my treasure of knowledge on this topic, ready?
Be a proper photobomber
Just get into the photograph with this kind of face. Hell yeah, without invitation. We're smiling on your back, uncle! The confidence kills me. I won't dare to do something like this, of course when in comes to do in FRONT! People might fear.
Ask relatives to get into his/her photo
It's the end of your duty. Relatives know how to ruin it! Family gossips never end, I mean NEVER! Is this a global issue? Say this is!
All alone posing? Nope, my uncle behind me is providing some support, thanks?
Kids are like, PRO!
Don't allow to sell balloons if I'm getting married someday! Or ban kids on stage, thoughts?
I hate hate hate when kids do this. Don't care if they don't understand how IMPORTANT is that to have good photographs. And their unintentional deeds couldn't be stand by me.
Tell them a lie
Take this as an evil thing. Tell them a lie and take a shot. You have done it! If they ask about looking pretty. Say hell yeah!
DISCLAIMER: Do this to only two kind of people. Best friends or best foe! Don't try this on homies, they can easily reach, BOOM!
High five to my twin!
Secretly on the flash! And see what comes up. Right, an ugly, eyes closed photograph. Betray me by this act, I won't forget you! Not even you, mum! Flash's purpose totally failed on this point!
Well, leave all thing behind. I love this kid and I'll forget him even if he does a balloon pose on my wedding.
You have more suggestions? I'm hearing!