No Homo!

This phrase , like many others,, started in the military. It's use is required PRIOR TO saying or doing ANYTHING that your peers might misinterpret, usually deliberately, in order to give you at least seven metric fucktons of crap for it, ad infinitum. The "No Homo!" claim Absolutely MUST be invoked beforehand; Saying, or worse, doing something that Could Be interpreted as "gay" (by Any witness in the immediate vicinity) without the protection of the invocation "No Homo!" may and Almost Always DOES result in the delivery of the aforementioned measurement of crap...from Anyone who later hwars of the incident.

The exclamation is simply to assure one's comrades in arms that they have nothing to fear from the oncomingwords and/or actions. In other words, they can't "catch being gay" or get "gay herpes" or have "gay dust get all over their shit", or any of the other, horrible fates that are more or less guaranteed without the prior invocation of protection.
The most common use is when a service member is preparing to say something personal, usually about their feelings or some other crap which the Department of Defense had not issued to them, such as, "No Homo, but...I love you guys".

For actions, the phrase is usually invoked prior to some sort of physical training, such as, "The next step (in hand to hand combat, for instance) is to get hip to hip with your partner, like this..No Homo!", immediately before demonstrating the move.

"...and, so, No Homo!...I wrapped my arms around his/her waist like this (as they begin to demonstrate it), and then..."
OR,
"I've been transferred to XYZ Unit, as of tomorrow. No Homo!, but I love you guys...You're my family!"