"I helped my uncle jack off a horse" is grammatically correct, like most puns.
"I helped my uncle Jack, off a horse." is actually brutal fail.
the difference is that in the first statement uncle jack is a compound noun, combining a common noun with a proper noun. If the uncle's name were Tom nobody would bat a lash at it because the statement is in fact grammatically correct the way it is.
the only problem is that jack off is also a compound noun, and if the statement were indeed meant to imply your uncle is into beastiality then that confusion could easily be dissipated by hyphenating jack-off, however, given the context, uncle jack clearly takes priority and it's obvious the statement is saying something innocent.
the second statement reads more like "I helped my uncle [whose name is Jack] off a horse." Because it reads as such, there needs to be a comma after uncle for it to make any fucking sense at all for there to be a comma after Jack. this part is so elementary i don't even going to explain it further.
"I helped my uncle Jack, off a horse." is actually brutal fail.
the difference is that in the first statement uncle jack is a compound noun, combining a common noun with a proper noun. If the uncle's name were Tom nobody would bat a lash at it because the statement is in fact grammatically correct the way it is.
the only problem is that jack off is also a compound noun, and if the statement were indeed meant to imply your uncle is into beastiality then that confusion could easily be dissipated by hyphenating jack-off, however, given the context, uncle jack clearly takes priority and it's obvious the statement is saying something innocent.
the second statement reads more like "I helped my uncle [whose name is Jack] off a horse." Because it reads as such, there needs to be a comma after uncle for it to make any fucking sense at all for there to be a comma after Jack. this part is so elementary i don't even going to explain it further.