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1.
A man with a large penis and massive testicles
A jumbo Jet refers to the fact that the owner of the afore-said jumbo sized tackle is able to force a correspondingly large amount of semen from it during ejaculation
slapper:
Fuckin ell that were a feller I had last night let me tell ya! That were a proper fuckin jumbo jet I ad flying into my terminal 5 last night
by stainesmassive April 05, 2008
 
2.
An extremely massive person.
"Her? She's a jumbo freakin' jet!"
by Caltag February 02, 2004