It is what some absurdly macho, homophobic fucks do when they give a statement that they fear will be interpreted in a homosexual way. From UrbanDictionary.com :
So naturally, being a guy with an entirely inappropriate and Nabokovian love affair with the English language, naturally I have to test the limits of No Homo, as in, just how gay of a statement is it a free pass for? Watch, ye mortal fucks, as Our Hero pushes this Magical +4 Talisman Against Appearing Queer to the very limits and beyond.
I LOVE THE PENIS. NO HOMO.
MAN, I COULD USE AN ENGORGED PULSING DICK IN MY VIRGIN ASS. NO HOMO.
YOU KNOW WHAT MAKES ME HAPPY? SUCKING BALLS. NO HOMO.
DOES ANYONE WANT TO WATCH 16 CANDLES? NO HOMO.
SO, KNOW WHERE YOU CAN FIND A TRUCK STOP GLORY HOLE? NO HOMO.
CUM IS DELICIOUS. NO HOMO.
Well that is all I have for now. Did it look gay to you?