You people, do you know that challenging each other on the
expressway is very dangerous? You endanger other road users!
I saw so many times; either two cars, or one car and a taxi, or,
two vans, or one van and one lorry. Both leap frogging one another,
cutting in each other's way. If one decides to jam brake, everyone
else behind, will become victims.
It's selfish!
Like I said, get a digicam that can do video recording, plus a
flashgun. No need to challenge each other. Let the party in front
wonder what you have done with that flash of light, and also, with
the video recording of his/her beautiful license plate and the way
he/she drove. Present it to the Traffic Police, let them deal with
these sorts of idiots.
Don't become one, yourself!