You can stretch a condom over your entire leg. Those guys aren't "too big" for condoms. They're feeding you a line of BS. Here's the Buzzfeed article of it:

http://www.buzzfeed.com/rossalynwarr...-bi#.swrgKJmVN

If they won't wear a condom, don't sleep with them. They're endangering you and you need to be sure to protect yourself.