This is a really good question, I'll give it some thought and get back to you asap.
:ETA:
One must consider which martial discipline would be toughest to beat, but also which produces or attracts the largest, toughest, and most violent fighters.

I'm 99kg, just under 2m tall with quite a solid jaw, but almost anyone under 18 is going to have significant advantages over me in terms of speed and stamina, a martial arts champion especially so...

High school seniors, no chance. Juniors, maybe.

I'd like to think I could beat anyone under 10, but I've seen some fast and vicious little boxers who could properly knock me out with a lucky or well timed hit, and I've seen some chunky judoka/rikishi who perhaps outweigh me, so I'll drop it to anyone under 9...

But there must be some 8 year old submission artists out there, so I can't guarantee that one couldn't trip me up and lock me into something I'd instantly tap out to, so let's drop it to somewhere around 6.
( brb Monkhouse Stampede, Mon 15 May 2023, 22:13, archived)

no it's about fighting not dating

( mofaha ┐( ˘_˘)┌ ʅ(́◡◝)ʃ, Mon 15 May 2023, 22:57, archived)

idgi

( brb Monkhouse Stampede, Mon 15 May 2023, 23:26, archived)

I think that's how most of them start

( Turtle Power & Knuckles, Mon 15 May 2023, 23:28, archived)

They ask for directions to the fictional town of Suckham, which is pronounced "Suckem"

( mofaha ┐( ˘_˘)┌ ʅ(́◡◝)ʃ, Mon 15 May 2023, 23:39, archived)

isdgi

( brb Monkhouse Stampede, Mon 15 May 2023, 23:47, archived)

Ok, forget it. Any idea how I can get to Suckham from here?

( mofaha ┐( ˘_˘)┌ ʅ(́◡◝)ʃ, Mon 15 May 2023, 23:49, archived)

Excuse me? The quickest way to Suckham?

( mofaha ┐( ˘_˘)┌ ʅ(́◡◝)ʃ, Mon 15 May 2023, 23:54, archived)

We just can't seem to find the way to Suckham, we've been at this hours!

( mofaha ┐( ˘_˘)┌ ʅ(́◡◝)ʃ, Mon 15 May 2023, 23:56, archived)