inverted, reverse, opposite, wicked
逆 centers on going against the expected direction or order: something inverted, reversed, or opposite. The sense of wickedness extends this idea to morally going against what is right.
逆 combines 辶 (movement) with 屰, which likely depicts an inverted person or something upside-down, together suggesting going against or opposing.
The movement radical 辶 surrounds 屰, which looks like an upside-down person. Picture someone walking in the opposite direction, going against the flow.
For ギャク, imagine a rebellious yak walking backwards: gyak -> ギャク, and the yak's reverse movement captures the kanji's meaning.
reverse; opposite
reversal (of a situation); turnaround; turnabout; turning the tables; sudden change; comeback
to go against; to oppose; to disobey; to defy
treason; treachery; mutiny; rebellion; insurrection
counterattack
inverted; upside down; reversed; back to front
underhand grip (e.g. in gymnastics, etc.)
retrogression; reversal; relapse; doubling back; backtracking
backward flow; backflow; countercurrent; reflux; regurgitation
backward movement; reverse movement; going backwards; retrogression; going in the wrong direction; going against (e.g. the times); running counter to
adverse circumstances; unfortunate situation; adversity
inverted; upside down; reversed; back to front; wrong way round
being resented (by someone one holds resentment towards)
handstand; headstand
paradox
going into a frenzy; flying into a rage
counting backwards; calculating backwards
one's superior's anger
irreversible
headwind; adverse wind