It will be very apparent in the way they treat you or try to avoid you.
If they avoid you
Ok, there are many approaches to this. 1:send them an anonymous email 2:have a friend say a bunch of names to them and if your crush is stupid he/she's eyes will get big when your friend mentions...
Give it some time and find something to keep you distracted. Eventually, you'll get over them. :)
when they stare at your boobs.