"Lock" the champion u hover in the end of the timer so your team cannot ban it

No. I can ban what I want. Sorry if I don't trust your chances of last pick cho'gath.

If you don't want people banning your champ stop trying to last pick Zac/Yas/etc.

Yes, give trolls more options to mess up your games? New champion coming out? Have it locked out so that the enemy team has a higher chance of taking it. Person who looking through their most recent games show they are constantly feeding with said champion? Lock it so you can get away with it yet again.

There is more problems that can be caused by this than actually solving. In the perfect world something like this could work, but sadly it wont especially not for a game like this!

most ppl troll ban your champion cuz they have lacking brain cells putting such lock will prevent flaming if someone bans someone's desired champ they both will flame and eventually one of them will troll the whole game.

This is an interesting debate. On one hand, you have a stubborn last pick who wants a must ban/pick champion. On the other, you have a first pick who can take such a champion but gets banned because of troll-y teammates.

Ignoring the fact that people want to ban a "first pick or ban" champion despite a late pick intending to play it (and believe it or not, we don't all own every champion. I can't first pick most power picks for you) - there's also the simple point that sometimes you're not thinking straight in the intent/ban step and accidentally intent the champion you wanted to ban. I've done it before. I just ban them in the next step, then show who I meant to actually intent afterwards. Can't do that if the champion gets locked out of bans though.