It turns out that before he made the 1999 hit with his cousin Marquis "DaKidd" Collins, Sisqo never even saw a thong before. "I had never seen one before," he told Billboard. "Apparently none of my friends had actually seen one, before because in 1999, there wasn’t a whole lot of thongs being worn unless it was in some sort of swimsuit ad."
He continued: "I just remembered first seeing one and it was like... you ever seen The Ten Commandments, when Moses went up and his hair was black, and then he came back down and his hair was all silver? That was literally the joke I was making with [my] silver hair. [The thong] was stone tablet-ed into my mind."
Then, the R&B vet spoke about the "dumps like a truck" line. Some odd people have believed that he was speaking about poop.
"Anybody that was trying to make a joke, the context of the lyric does not say anything to the effect of she took a dump like a truck or nothing like that," he said. "She had dumps like a truck, so that joke is old. Nobody can use it no more. You sound stupid. Stop it."
This wasn't the first time that Sisqo explained this lyric. In a previous interview with Stereogum, he said: “That would mean I was some kind of fecal freak, What I was really referring to was — a dump truck when it backs up, it’s like, ‘beep, beep beep.’ So, ‘she had dumps like a dump truck’ is, like, when girls do a booty dance move and they look back at their butt. She’s like a dump truck back-back-backing it up.”
Read can read the entire "Thong Song" story here. It's a really good read.