A guy knows he's in love when he loses interest in his car for a couple of days.
[Tim Allen -RD]
The reason we say "fell in love" is that it makes it sound more like an accident. Men act like, "I was walking along and fell in love. I tried to get my boys to pull me out, but I got all tangled in ropes and sticks, and I couldn't break free."
[Chris Rock -RD]