Forgot to Say Checkmate!?!?

Easy! Online, if you checkmate somebody the game stop and sign will pop up saying that ---- won by Checkmate. In real life or over the board. You opponent should  notice, but if they don't and they make a move, you should point It out to them

When playing chess with a real board it is considered bad form and rude to announce "check" or "checkmate".

Normally, I would just put my hand  out for a handshake. It's  way more respectful that way.

The game ends when the checkmating move is complete. Saying "checkmate" is not required.

Actually it would be nice to have an article stating when words are actually required:

1. Adjusting pieces

2. Offering a draw

3. Claiming a draw by repetition, or 50 move rule

4. Resigning 

5. Explaining after the game, why you lost and how you would have crushed your opponent under any other condition, a rematch demand, accusations of cowardice, dishonor, mere wood/plastic pushing, derogatory references to their family line... 

7. Yelling crazily  as you knock off all the pieces in a great and rage  filled resignation.

I think not. Tipping your King over and offering to shake hands is tantamount to resigning, and requires no verbal component.

True, GMs  don't  speak. Almost not at all.

So they're mutes?

If you forget to say checkmate and you offer your hand to shake hands, then it'll be a draw because you offering your hand counts as a draw offer, instead you should scream "checkmate" at the top of your voice and dance around your opponent while chucking insults at him.

Never offer non verbal draw when you accidentally knock over your king.

In a tournament in Zagreb back when Yugoslavia was still a thing, one of the players from Yugoslavia offered his opponent a draw and held out his hand. His opponent (from Mongolia) looked at him in bafflement, looked at his extended hand, then shook hands and got up from the board. The Mongolian spoke a few words to the TD, then both players then left the playing hall.

It was only the next day, when the players reconvened for the following round, that the Yugoslav realized that the game had been officially scored as a loss, not as a draw. The Mongolian player hadn't understood a word that the Yugoslav said, and thought he was resigning.

The Yugoslav player protested, and the matter was referred to the appeals committee. It was a difficult case, but the Yugoslav player carried the day when he haughtily pointed out that no Yugoslav would ever shake hands with a man who had just defeated him!

He shouldn't have held out his hand. That means the game is over. Still, when I resign I stop the clock before, just in case.

If Maurice Ashley were there, he could have used the smoothness test to determine if it should have been a draw or otherwise. 

i often forget to say checkmate.

maybe if i played better i would have the opportunity.

HI I AM NEW TO THIS SO PLEASE TELL ME THAT 
DO I NEED TO SAY CHECK AFTER I CHECK MY OPPONENT WHEN PLAYING CHESS ON-BOARD..
PLS TELL ME I AM A BIT CONFUSED...

No. Announcing check is not required.

It is required to say checkmate if you don't say it then you lose and it is required for a redo