Oh yeah, I've been there many times. I've been playing since 2010 and I can tell you the worst times:
Just recently, when the Keystones first hit live; couldn't play him for a long ass time and had to hope he wasn't banned and that I was first pick.
Been a lot of times Gragas has been in the spotlight; back when he was still in his pre-rework state, I use to run him as a tank due to Drunken Rage's original stats: it granted mana, an AD steroid, and percentile damage reduction over a duration like a mini-Alistar ultimate. Then people started playing him as a mage and he got banned a lot, then he got rework several times, to the point he's now almost exclusively jungle; that's my worst role. I've tried laning with him, but I just can't seem to pull it off, letting all my numerous Gragas skins collect dust.
Malzahar was my go to mid laner before the rework and for the longest time after his rework, I couldn't play him because he either got banned or someone else picked him before me. Its not as bad now of course.
Proxy Singed became all the rage, so he became a consistent ban; he's fine now, but he has very clear counters so I don't pick Singed as often as I want to.
Urgot holds a special place for me, but then he's picked in the LCS and suddenly nerfs out the ass after a long time of neglect and him becoming a popular pick/ban for all the flavor of the month sheeple.
This one hurts the most; when Zed first came out, everyone proclaimed him garbage because he was hard to build properly and he just didn't seem to have enough damage. I loved Zed, his kit, his themes, I was determined to play him even if he did suck but then the next season rolled in with the new AD itemization with Zed quickly becoming a popular pick to this very day. As much as I loved Zed, playing a champion that everyone and their grandma plays is so annoying and boring.