Seagel is a washed up Never-Was. I would mud stomp that pony tail right off his ass.
Leonardo - I can't even picture him as anything remotely like a threat to me.
Vin Diesel - perhaps, but as a bouncer he was never really in an one on one fight.
I would probably have a tough time with that Duncan guy from Scorpion King / Green Mile or with actor who played Zeus.
Jackie Chan and Jet Li won't ever be mentioned. They are just way too far out of the league in fighting skills as most celebrities.
The ones I would love to pick a fight and bash their faces in, would be:
George Clooney
Russell Crowe
Oliver Platt
Martin Lawrence