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1.
An attempt during vaginal intercourse for one bro to secretly switch with another between thrusts. Thus the women has little to no idea that she is being railed by a different man.
"Catherine said you pounded her for over an hour last night! How did you do it?"

"Oh, my bro and I pulled a swap-in."

"Craig was doing this chick froggy style but starting passing out. Jon, unselfishly, swapped-in for him."
by swappers December 03, 2011