No, not the G spot - that hard to find spot on a woman that will transport her to ecstasy.
In fact, the "P spot" refers to the prostate gland - which, when properly stimulated, can have a similar effect on men. Gently massaging the prostate either by inserting fingers or a toy into the anus or by massaging between the testicles and anus can send a guy literally wild.
It's seldom talked about in sex ed - probably because it's associated strongly with gay sex, a topic not all teachers are willing to go into. But the prostate really is a powerful erogenous zone for men. P spot stimulation alone can lead to orgasm and ejaculation - something doctors sometimes use to reliably obtain sperm samples.
An internal prostate massage tends to be more effective than external - which is often where anal toys such as plugs and beads come in. Plugs and beads are often better as an introduction to anal sex than penetration or pegging - mostly because they're smaller than a penis or dildo and easier to insert (although lube is still essential). As the P spot is in a different place on different men, some might find a particular toy is better than another, or it might take a few tries to get the best results - it's definitely easier to find than the G-spot, though. Butt plugs are generally used to add prostate stimulation to other sexual activity and thus can help with a more intense orgasm and greater stamina.
A lot of straight guys don't like the idea of anything up their ass and might be reluctant to try an internal massage - but if they do they might realize exactly what they've been missing. It absolutely does not mean you're gay - it just means you're a normal guy (Of course, there's nothing at all wrong with being gay).
So, why does a prostate massage do the thing? It has a lot of nerve endings in it, for one thing. The prostate actually plays a key role in sex - it produces most of the fluid in semen (as opposed to the actual sperm). As it contracts during ejaculation, it's not a surprise that it can be stimulated - it plays a role in orgasms and fertility even if you aren't looking for it.
So, try it or get your partner to try it. Make sure to use lube - and make sure the lube is rated for anal play (some lubes are only designed to supplement natural vaginal fluids or to use on toys) - and discover an entire new level of pleasure.
