Yup is a generic term of agreement issued often by a non-listening party, typically used while performing an additional important task, such as watching tv.
If you are the yupper, by yupping someone, you are not bound in any sense by your agreement, since you didn't hear what it was you were agreeing to. If you are later asked to perform the task, you then have the option to admit that you had yupped the person and ignore the task, or pretend that you had really listened & just go along with the yuppee.
If you are the yuppee, and you recognize that you are being yupped, you can call the yupper's actions & state "you're yupping me" or "I'm being yupped", whereupon the yupper may admit the yupping action and feel mild embarrassment, but there will be no permanent damage.
yupping, being yupped, yupper, yuppee are all derived from the root 'yup'
Woman: Oh I got some great shoes at the mall, do you like them dear?
Man (watching tv): yup
Woman: so we're going to go back later, are you coming with us?
Man (watching tv): : yup
*2 hours later*
Woman: ok, let's go
Woman: to the mall? you said you'd come with me later?
Man - option 1: oh, I was just yupping you, I'm staying here
Man - option 2: yea that's right, let me grab my coat