Somewhere out there, there are typos that I am responsible for. I will find these typos, whether they appear in old essays for my fifth grade class or on the Gog forums. Then, I will go back in time and correct them one by one.

The most legit use does not belong here sir!

But yeah I wish I tapped that and studied this. Man that was dumb.

Very lame would be to go back and (passively) watch yourself make the mistakes you still kick yourself over now

With a very loose understanding of history, going to congratulate the man who killed Hitler

Going back in time to write yourself a note so that you make different meals today

Going ahead in time to see when you die,and then not coming back because you died...

Going forward in time to watch "Jaws 19" and discovering the awful truth.

Travel back to be the first person to carve their name on devil's tower?

I had approximately 254 different ideas to use for this question. After reading through the answers here, I see that every one of them was mentioned already.

So my use for a time machine would be to go back in time just long enough to post all the funny ones first. That way I could get just enough positive rep points to justify the massive amounts of energy required to actually build and use the time machine itself.

Every one of you can go FLUX yourselves.

I'd use it to slap myself for thinking I could open a coconut with an axe, and not leave a mark on the finger.

I could also slap myself really hard for skipping my studies at college, but to be honest I think the first one is more lame-er.

Playing the Solitaire and every time you made a mistake, you would use the time machine to go back in time.

Maybe Life is strange? (Main character reverses time to undo her camera getting broken)

Overkill so hard that even Doc Brown said that was serious shit.

For more lame time machine uses watch The Girl who leapt through time.

OOOhhhh! I must watch!