This is for the way they most severely affected our season, our program trajectory, prestige , our fanbase, whatever you choose?
My top list with reasons listed
1939 - USC - Broke our unbeaten, unscored on streak
1940 - Boston College - cost us undefeated season and consensus NC
1950 - Miss. State - cost us consensus NC
1956 - Baylor - cost us consensus NC
1965 - Ole Miss - cost us major bowl and chance at NC
1966 - Bama - cost us chance at NC
1967 - Oklahoma - cost us chance at consensus NC
1968 - Texas - could have elevated our program to elite in eyes of media instead of Bama
1969 - Ole Miss - cost us chance at NC
1970 - Auburn - cost us chance at NC
1971 - Bama - cost us chance at NC
1980 - UGA - had the game won twice and our fumble gave them their only NC in modern history
1983 - Ole Miss - cost us a major bowl vs Texas
1985 - Florida - cheating gators cost us a chance at NC
1987 - Boston College - cost us a chance at major bowl
1989 - Bama - cost us chance at NC
1990 - Bama/N. Dame - cost us chance at NC
1992 - Arky/SC - either cost us 3 game lead over Fla in initial SEC title game
1993 - Florida - cost us major bowl/SEC title
1995 - Florida - cost us major bowl/SEC title/chance at NC
1996 - Memphis - cost us major bowl
1997 - Nebraska - cost us chance at NC
1999 - Arkansas - cost us SEC title/chance at NC
2000 - Florida - cost us SEC title
2001 - LSU - cost us SEC title/chance at NC
2003 - Auburn - cost us major bowl/chance at SEC title
2004 - N. Dame - cost us major bowl and hurt QB
2004 - Auburn - cost us SEC title and major bowl
2006 - Florida/LSU - cost us SEC title/major bowl/chance at NC
2007 - LSU - cost us SEC title/major bowl
2014 - Florida - missed opportunity to overtake Florida rebuilding
2015 - Oklahoma/Florida/Bama - missed opportunity to "be back"
2016 - Vanderbilt - cost us the Sugar Bowl