I ever encounter... i was walking in crowded orchard underpass
MRT. Some dude behind me stepped on the back of my slippers, then
when i lifted up my feet i almost tripped. I'm wearing those
Havaianas rubber flip flops.
Coz that idiot is tailgating me. And its not like my slippers
are very long or big. He apologized but i turned round n glared at
him. Then I walked somewhere else where he is not behind me.
That time i was with my friends, and i told them what happened.
Guess what? They all started to disturb me by stepping on the back
of my slippers. Good thing i scolded them firmly not to joke
around, as tripping n falling on the floor especially in a crowded
place is not joking matter.You could get hurt as well as the people
around you.
And now if anybody does that to me, i feel like taking my
slippers n slapping their face with it!
How old are your friends?
How come you're so dumb to even tell them about it?
Do you expect them to take revenge on your behalf?
Please.........don't be NAIVE. 
You are not even important to your friends, and you're easily
replacable.