How to tell if a guy is a virgin?

What are tell tale signs he is a virgin not through seeing how he is in the bedroom (example: how he speaks, or what he does, how he acts in all other topics and aspects of life besides just getting him into bed and actually putting it to the test)?

An easy way to find out if he's a virgin or not is a technique that's not well known but I will tell you it anyway as you may find it useful. First of all, sit down with him, and have a conversation. Make sure it's a normal conversation. However, when you want to find out if he's a virgin or not, repeat the following line:
"Are you a virgin?"
Depending on his answer, you should be able to figure out his virginity status.

Well obviously straight up asking can get straight to the point. But often is considered invasive and rude overstepping boundaries and he is pretty to himself about a lot of things.

Sneak up behind him, cup your hands and shout "SEX!" at him. If he screams and runs away then he's probably a virgin.
What are you seriously expecting the answer to be here? There aren't any telltale signs of how often someone has had sex, aside from when they're talking about the sex they haven't had. The only way to know one way or the other is so to ask. If you don't feel able to do that, then don't. Is there a particular reason why it matters? You've referred to finding out by getting him into bed, but there's no particular reason why that would give you a definitive answer either. Someone who has not had sex but has had other intimate experience can be much 'better' at sex than someone who's had sex multiple times but has been much less conscientious about it, or has had a less supportive partner.

Sneak up behind him, cup your hands and shout "SEX!" at him. If he screams and runs away then he's probably a virgin.
What are you seriously expecting the answer to be here? There aren't any telltale signs of how often someone has had sex, aside from when they're talking about the sex they haven't had. The only way to know one way or the other is so to ask. If you don't feel able to do that, then don't. Is there a particular reason why it matters? You've referred to finding out by getting him into bed, but there's no particular reason why that would give you a definitive answer either. Someone who has not had sex but has had other intimate experience can be much 'better' at sex than someone who's had sex multiple times but has been much less conscientious about it, or has had a less supportive partner.