Smith, who made her emotional farewell to the breakfast programme after 17 years last week, claimed that her fellow presenter came across as dour after his favourite football team lost a match.
"I'm not sure Eamonn is a huge fan of early starts. I've got friends who one approaches with caution when they have PMT, but they are nothing compared to Eamonn when he was in a mood," she told the Daily Mail. "I learned to keep a low profile when Manchester United lost a game."
However, the 51-year-old praised Holmes's broadcasting qualities, saying: "And yet, he makes me laugh out loud and is a brilliant presenter who simply has a knack of knowing what will work on television. When Fiona [Phillips] joined him on the sofa [in 1997], things calmed down."
Smith also admitted that Holmes's high-profile row with co-host Anthea Turner in the mid-1990s was "possibly the most uncomfortable period of [her] time" on the programme.