"If the truth were known, many, many senators would be very envious, as I am, and I would even think the presiding officer, about that hair of Ben Nelson's," Reid said on the Senate floor.

"I mean, that is a mop of real hair," he continued, adding that many believe Nelson is wearing a toupee. "It's his hair. He'll pull it for you any time just to show you that it's real.

"I mean, he has hair like a 15-year-old."

In 2007, Nelson's hair got some attention after it went from a helmet of gray one day to a brunet the next. Nelson knew it didn't look so natural, and he appreciated that Sen. Susan CollinsSusan Margaret CollinsSenate Dems hold floor talk-a-thon against latest ObamaCare repeal bill Ryan: Graham-Cassidy 'best, last chance' to repeal ObamaCare Collins skeptical of new ObamaCare repeal effort MORE (R-Maine) didn't point out the obvious after they had a long conversation.

“Let me just thank you for not saying anything about my hair,” Nelson said at the time.

Collins doubled over in laughter.