Folding SB and BB shows sub par cards?

Ever since I have started playing online I have noticed that if I fold the sb to the bb and let them take the pot they will sometimes show me sub par cards. Just what are they trying to accomplish with this move?

I ask this because it seems to me they are trying to get me to be more aggressive but it doesn't make sense because if I make a move against their blinds or call the rest it is because I like MY cards. Their cards shouldn't even matter unless I am reraised.

Any opinions would be appreciated on this matter.