When someone attempts to say, "Yeah, but (...)" etc, it will sound as though the two words are often combined into one, as if it were a small woodland animal. Hence, you obtain "Yeahbut". It is even more so funny when they say "fucking" afterwards, making it sound as though they plan on having intercourse with a small woodland animal.
"Yeah, but I disagree."
"Yeah, but fucking, I was totally not going to go."
"Yeah, but you forgot to include me."
"Yeahbut fucking is strictly NOT allowed in most states."
A classic law school student -ism. Usually employed right before the speaker dives into an argument that has no sound basis in logic, reason, or this universe.
Le Frankliham - "Yeahbut, all I'm saying is we should ban all the gunz."
Reasoned opponent - "How did you get in here?"