Essentially, heteroflexible. A person who is predominantly heterosexual (NOT homosexual or bisexual) and attracted to and desire to engage in sexual activities and relationship only with the opposite sex--but, given the right rare circumstances, such as an extended sexual drought, a rare and temporary same-sex attraction, or a reduced lack of inhibition from sufficient tequila or other substance, will engage privately and discretely in certain and limited sexual activities focused solely on mutual physical stimulation and release with the same sex, with neither participant fulfilling or desiring to fulfill the role of the opposite sex.
Basically, this involves a gay "experience," not an overriding preference for the same sex or a gay lifestyle. For men, this generally means limited non-sexual caressing and no mouth-to-mouth kissing or (especially) anal sex. Some may find limited oral to not be objectionable. YMMV.
For women, it generally means "lipstick lesbian" activity as occurs in college or among good friends (or on a fun-filled vacation) with no strap-ons or monster double dongs, although some toys and small vibes might enter the picture as an enhancement.
Some activity of this nature can occur in a traditional heterosexual marriage or relationship when the partners decide to extend it to a threesome scenario, such as MFM or MFF. Usually this activity is of a one-time nature, with no repeat performances or long-term relationship ensuing. The participants are not likely to make the encounter public, as it is not an activity they generally seek out.
Gay guys and gals may not care much for a g0y person just dabbling, or may take it as an insult that the g0y dabblers might be homophobic or judgmental, or look down on people that practice full penetration, but it is not the case. Why would they fear or judge an activity they have engaged in? Bottome line, the g0ys just don't fit the profile of being gay. It is similar to a gay fem gal that only likes other gay fem types, not the Butch--it's nothing person, it's just not what appeals to them, period.
Most guys are not gay or even bisexual, but a lot of them might occasionally be g0y! I guess you can call me g0y, because I'll take a handjob anywhere I can get it, even if I have to reciprocate (it might be a fun challenge)!