Someone is said to be 'playing footsie' when they are touching and rubbing their legs against another persons in a sexual manner, often under a table. More often than not, a lady will initiate it. It can not be done with shoes on as it needs skin to skin contact to work the best.

A game of footsie is often incorporated into movies, where a lady with a stocking covered foot with start running her foot against a guys leg while they are both in a restaurant (or diner). She starts touching her toes against the lower leg and then rubs her foot up the leg. It is often accompanied by a playful, sexual stare and direct eye contact is made.

There is a few different way to spell Footsie, including Footie. The reason why the version 'footie' is avoided as it is the name of a sport in some countries.

Importance of touch

When flirting with the opposite sex, touch is a very important tool in obtaining an emotional connection. It could be with your hands, feet or another part of you body, but if both parties enjoy the touching, you will both have a stronger emotional connection.When used incorrectly, it could destroy the chance for a relationship.

Variations

There are many variations to a Footsie. One is call Football. This is when a girl runs her foot up her partners leg and moves it over her partners crotch. 

Oh and if you are wondering what the phrase "I want to play footsie with you" is in French, I think is along the lines of:

Je veux faire du pied a toi!