Possible, but not usual. Actually the only expression that I can think of in which it could be considered an adjective is "pity party", which is how someone might describe sarcastically someone else's seeming request for sympathy. It's a noun used as an adjective to answer the question "What kind of party?" -- "A pity party." (Just like the noun "house" can be used to say "house party" as a kind of party.) Pitiable and pitiful are the normal adjectives related to the noun "pity" and describe things, events, or situations that evoke or cause pity.