This list below only is from TAR14 to 18/UB, because those were the five seasons that I actually have seen in full.
TAR14 - Jaime, Mark & Michael, Jennifer (for having Preston carrying you to the First Pit Stop, especially), Luke & Margie (mostly Luke)
TAR15 - Lance, Ericka, Sam & Dan, Mika & Canaan
TAR16 - Joe (for many, many things, and as such, you give a bad name to a certain group of people), Caite & Brent (more Caite than Brent), Jeff & Jordan (purely for plain stupidity), Carol & Brandy (for dragging U-Turn gate for far too long), Louie & Michael
TAR17 - Nick (for being a quitter and being flat out stupid at times), Chad, Thomas (not annoying IRL), Katie & Rachel (not annoying IRL either), Mallory to some extent (please don't bring her inside a poker room, thank you), Kevin to a little extent (put some belief in your father, like TAR12 Nick did to his grandfather - and even Don is older than Michael)
TAR18 - Kent & Vyxsin (both equally annoying), Flight Time & Big Easy, Ron
As for previous seasons, Jonathan and Kendra (both TAR6) are on the top of my list for annoying. And yes, there are probably other racers that have been annoying through the seasons, but I didn't watch most of those seasons anyway.