Trashy? I don't know. Depends on the environment. If you're at home or just around in public, I doubt that anyone gives a shit. I think it might be considered "trashy" at work or church, maybe. But considering some guys walk around with their jeans sagging off of their asses, what you described is probably not an issue at all.
I don't understand this logic of panty-lines showing being trashy? Nor do I understand the logic of wearing /more/ revealing panties with leggings or yoga pants. I'd think you'd want to wear less revealing panties with tighter clothing... I don't like thongs either, I wear bikini's or boyshorts no matter what I have on.