You might want to think of asking people out as asking for the option of developing and acting on mutual interest, rather than saying "Let's suck face now".

The cost of rejection is usually extremely low. You feel slightly awkward and disappointed for a few minutes, then go back to acting less flirty than the average Victorian priest.

I'm bad at reading people, but if you're just asking "Are they at all interested?", asking them out is the way to go. And if you get a "yes" to that, it creates a situation where it's acceptable to test more or less directly how interested they are.