When should you tell someone they suck at a sport

I fluctuate between a 6 and 8 on looks daily, above average athlete with a great sensor of humor, and master chef on a grill. But even I know when I simply suck at something. Whether its celebrating another meaningless coed kickball homerun or trying to water ski at 30 years old, we all need to realize there are some things we just cant do as well as others and our friends should tell us. 

For me it includes a friend who we will name Jeff in our weekly golf foursome. We usually get a full 18 holes as we all work sales jobs as the guys who never hit their numbers. Since it is Friday golf the scores are more relaxed but who doesn't like to win. We have been playing together for the past year and I have never seen Jeff break a 100. The rest of us are low 80 to mid 80s scores so you see why we rotate cart partners.

Is there a reasonable way to tell Jeff he sucks at golf. Like buddy you keep telling yourself to keep your head down will magically fix your 7 chips from 120 out. Its a moral dilemma as we all like the guy and he always has a new pack of 27's shorts but enough is enough.

So is it on Jeff to realize he is holding me back from shooting a 74 or do I have to Gretchen Weiner this fool.