Why is it unlucky?

[anotheoldgit]

Why is it deemed unlucky to say 'thank you' to someone that picks up your glove and hands it back to you when you have dropped it?

[Quizmonster]

There may possibly be some connection with the fact that a glove was involved in a challenge to a duel in times past. Thus, we have phrases such as 'throw down the gauntlet' = make the challenge and 'pick up the gauntlet' = accept the challenge. So, the to-ing and fro-ing of gloves had an element of animosity involved.