Advise

When you board a train and there is only 1 seat left with 2 guys sitting at each side, it is much more advisable for you to stand instead.

Well, guys can really occupy the seat. They take 1 1/4 of it.
Thus, through mathematical calculation:

1 + 1 + 1 = 3 seats.
guy + you + guy = 3 seats
1 1/4 + you + 1 1/4 = 3 seats
you = 3 - 1 1/4 - 1 1/4
= 1/2 seat.

This advise is only applicable for girls. As for guys, you just gonna become another ready-made sardine.