Asking someone to grab a cup of coffee is a classic and casual way to ask someone out. Whether it's considered "lame" or not depends on the context, the person you're asking, and the overall impression you make.
In general, asking someone out for coffee is a low-pressure and non-intimidating way to get to know someone better. It's a common approach because it allows for an informal meeting where both individuals can chat and see if there's a connection without the expectations of a more formal date.
The success of this approach depends on the delivery, sincerity, and the level of interest shown by the person asking. If you approach it confidently and genuinely, most people would appreciate the invitation. On the other hand, if it comes across as insincere or too generic, it might not leave the best impression.
Remember that communication and body language also play a significant role in how your invitation is received. Be respectful, attentive, and friendly, and the way you ask should be well-received by most people. But, ultimately, individual preferences and comfort levels vary, so there's no one-size-fits-all answer to what makes an approach "lame" or not.
If you're considering asking someone out for coffee, go for it! Just be yourself, be respectful, and be prepared to take their response gracefully, whatever it may be.